<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a0817f-1d7f-7a2d-b595-9a0db39b308d,g:84ee5f57-5653-48e3-9089-25b0ade5d709-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://tmc.com/role/CondensedConsolidatedStatementsofChangesinEquity" xlink:type="simple" xlink:href="tmc-20260930.xsd#CondensedConsolidatedStatementsofChangesinEquity"/>
  <link:definitionLink xlink:role="http://tmc.com/role/CondensedConsolidatedStatementsofChangesinEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7f82-a222-9d8932adf16d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a0817f-1eb9-7544-b24d-22e1360708ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7f82-a222-9d8932adf16d" xlink:to="loc_us-gaap_StatementTable_01a0817f-1eb9-7544-b24d-22e1360708ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a0817f-1eb9-7e11-b2dc-9e233e8beb37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a0817f-1eb9-7544-b24d-22e1360708ea" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a0817f-1eb9-7e11-b2dc-9e233e8beb37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7e11-b2dc-9e233e8beb37_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a0817f-1eb9-7e11-b2dc-9e233e8beb37" xlink:to="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7e11-b2dc-9e233e8beb37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a0817f-1eb9-7e11-b2dc-9e233e8beb37" xlink:to="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a0817f-1eb9-7e34-8261-667e1f0fc2b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:to="loc_us-gaap_CommonStockMember_01a0817f-1eb9-7e34-8261-667e1f0fc2b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a0817f-1eb9-7615-87ce-d7668f73c88f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a0817f-1eb9-7615-87ce-d7668f73c88f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a0817f-1eb9-7988-9565-109f9e5cb751" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a0817f-1eb9-7988-9565-109f9e5cb751" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a0817f-1eb9-7b9c-89ec-5e23e6a708a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a0817f-1eb9-7d14-a58d-3c3543eba92d" xlink:to="loc_us-gaap_RetainedEarningsMember_01a0817f-1eb9-7b9c-89ec-5e23e6a708a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a0817f-1eb9-757c-9e78-d65e23748607" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a0817f-1eb9-7544-b24d-22e1360708ea" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a0817f-1eb9-757c-9e78-d65e23748607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-757c-9e78-d65e23748607_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a0817f-1eb9-757c-9e78-d65e23748607" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-757c-9e78-d65e23748607_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-787d-88e2-76b8a9c9bd67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a0817f-1eb9-757c-9e78-d65e23748607" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-787d-88e2-76b8a9c9bd67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RegisteredDirectOffering2025Member_01a0817f-1eb9-7857-b493-3aa7b475e818" xlink:href="tmc-20260930.xsd#tmc_RegisteredDirectOffering2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-787d-88e2-76b8a9c9bd67" xlink:to="loc_tmc_RegisteredDirectOffering2025Member_01a0817f-1eb9-7857-b493-3aa7b475e818" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RegisteredDirectOffering2024Member_01a0817f-1eb9-7446-943c-4c0aa8aa6d11" xlink:href="tmc-20260930.xsd#tmc_RegisteredDirectOffering2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a0817f-1eb9-787d-88e2-76b8a9c9bd67" xlink:to="loc_tmc_RegisteredDirectOffering2024Member_01a0817f-1eb9-7446-943c-4c0aa8aa6d11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7472-9f4a-6d017311e552" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a0817f-1eb9-7544-b24d-22e1360708ea" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7472-9f4a-6d017311e552" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7472-9f4a-6d017311e552_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7472-9f4a-6d017311e552" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7472-9f4a-6d017311e552_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7d96-ae4d-fdb2b4eb42f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7472-9f4a-6d017311e552" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7d96-ae4d-fdb2b4eb42f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-7a7a-a17f-3b10c04ede38" xlink:href="tmc-20260930.xsd#tmc_ClassAWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7d96-ae4d-fdb2b4eb42f6" xlink:to="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-7a7a-a17f-3b10c04ede38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-75a5-9db9-836f533b0feb" xlink:href="tmc-20260930.xsd#tmc_ClassBWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7d96-ae4d-fdb2b4eb42f6" xlink:to="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-75a5-9db9-836f533b0feb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7f82-a222-9d8932adf16d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a0817f-1eb9-7cae-9f66-a4170eefb2e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_SharesOutstanding_01a0817f-1eb9-7cae-9f66-a4170eefb2e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a0817f-1eb9-7a2a-9465-e172948bbf69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockholdersEquity_01a0817f-1eb9-7a2a-9465-e172948bbf69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SharesIssuedDuringPeriodSharesPrivatePlacement_01a0817f-1eb9-7fe8-a2c2-c261d0c1a89a" xlink:href="tmc-20260930.xsd#tmc_SharesIssuedDuringPeriodSharesPrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_SharesIssuedDuringPeriodSharesPrivatePlacement_01a0817f-1eb9-7fe8-a2c2-c261d0c1a89a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SharesIssuedDuringPeriodValuePrivatePlacement_01a0817f-1eb9-7371-817f-f30f36547206" xlink:href="tmc-20260930.xsd#tmc_SharesIssuedDuringPeriodValuePrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_SharesIssuedDuringPeriodValuePrivatePlacement_01a0817f-1eb9-7371-817f-f30f36547206" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockIssuedDuringPeriodSharesRegisteredDirectOffering_01a0817f-1eb9-7282-a59b-6ad0fc02e076" xlink:href="tmc-20260930.xsd#tmc_StockIssuedDuringPeriodSharesRegisteredDirectOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_StockIssuedDuringPeriodSharesRegisteredDirectOffering_01a0817f-1eb9-7282-a59b-6ad0fc02e076" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockIssuedDuringPeriodValueRegisteredDirectOffering_01a0817f-1eb9-732f-8902-2a95d99faf25" xlink:href="tmc-20260930.xsd#tmc_StockIssuedDuringPeriodValueRegisteredDirectOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_StockIssuedDuringPeriodValueRegisteredDirectOffering_01a0817f-1eb9-732f-8902-2a95d99faf25" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a0817f-1eb9-766d-b463-a49200f53cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a0817f-1eb9-766d-b463-a49200f53cdc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a0817f-1eb9-7999-ba59-640b497675c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a0817f-1eb9-7999-ba59-640b497675c2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockIssuedDuringPeriodSharesWarrantsExercised_01a0817f-1eb9-7b8b-9b4d-5fa0b7b787fb" xlink:href="tmc-20260930.xsd#tmc_StockIssuedDuringPeriodSharesWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_StockIssuedDuringPeriodSharesWarrantsExercised_01a0817f-1eb9-7b8b-9b4d-5fa0b7b787fb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockIssuedDuringPeriodValueWarrantsExercised_01a0817f-1eb9-7c53-9a71-e41225773c80" xlink:href="tmc-20260930.xsd#tmc_StockIssuedDuringPeriodValueWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_tmc_StockIssuedDuringPeriodValueWarrantsExercised_01a0817f-1eb9-7c53-9a71-e41225773c80" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_01a0817f-1eb9-7838-bc21-f8600732a0e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_01a0817f-1eb9-7838-bc21-f8600732a0e4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_01a0817f-1eb9-7030-a0f7-79e21eed23ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_01a0817f-1eb9-7030-a0f7-79e21eed23ba" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a0817f-1eb9-73d1-9cf2-f9d0f934bddf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a0817f-1eb9-73d1-9cf2-f9d0f934bddf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a0817f-1eb9-7aca-a252-749c4432c6bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_01a0817f-1eb9-7aca-a252-749c4432c6bf" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a0817f-1eb9-74fc-a042-0c8ecd92b9a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a0817f-1eb9-74fc-a042-0c8ecd92b9a8" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_01a0817f-1eb9-7bfd-b4b0-c803ead58e42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_01a0817f-1eb9-7bfd-b4b0-c803ead58e42" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_01a0817f-1eb9-72a4-bb30-4e79c12c67cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_01a0817f-1eb9-72a4-bb30-4e79c12c67cb" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a0817f-1eb9-7507-9369-045b371e441c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_01a0817f-1eb9-7507-9369-045b371e441c" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a0817f-1eb9-7e94-a876-c8ff1640c7ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a18cb2-c22a-7436-8df9-31639872fff0" xlink:to="loc_us-gaap_NetIncomeLoss_01a0817f-1eb9-7e94-a876-c8ff1640c7ca" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a0817f-1eb9-7e82-9935-2a52ad898ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a0817f-1eb9-7218-a2f4-017ba15a41de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="tmc-20260930.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://tmc.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a0817f-1eb9-75ae-8197-cbd50bbf1f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_StatementTable_01a0817f-1eb9-75ae-8197-cbd50bbf1f2f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-79ea-a43f-7337c74d0ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a0817f-1eb9-75ae-8197-cbd50bbf1f2f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-79ea-a43f-7337c74d0ba5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-79ea-a43f-7337c74d0ba5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-79ea-a43f-7337c74d0ba5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-79ea-a43f-7337c74d0ba5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7c0d-a26f-31d637983009" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-79ea-a43f-7337c74d0ba5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7c0d-a26f-31d637983009" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-789f-86ec-37988850ed79" xlink:href="tmc-20260930.xsd#tmc_ClassAWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7c0d-a26f-31d637983009" xlink:to="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-789f-86ec-37988850ed79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-70f9-b655-2e21427c078d" xlink:href="tmc-20260930.xsd#tmc_ClassBWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7c0d-a26f-31d637983009" xlink:to="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-70f9-b655-2e21427c078d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a0817f-1eb9-7b82-a1bf-3793fb1326c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a0817f-1eb9-7b82-a1bf-3793fb1326c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a0817f-1eb9-72f7-8745-1c87911688c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a0817f-1eb9-7b82-a1bf-3793fb1326c3" xlink:to="loc_us-gaap_NetIncomeLoss_01a0817f-1eb9-72f7-8745-1c87911688c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:href="tmc-20260930.xsd#tmc_ItemsNotAffectingCashAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a0817f-1eb9-7b82-a1bf-3793fb1326c3" xlink:to="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_WarrantsIssuanceCosts_01a0817f-1eb9-7e2c-9c6c-e28ad6b89efc" xlink:href="tmc-20260930.xsd#tmc_WarrantsIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_WarrantsIssuanceCosts_01a0817f-1eb9-7e2c-9c6c-e28ad6b89efc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentForAmortization_01a0817f-1eb9-7c97-b2f0-85afad6fa968" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentForAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_AdjustmentForAmortization_01a0817f-1eb9-7c97-b2f0-85afad6fa968" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_01a0817f-1eb9-730b-b7f3-c1b6c000ab52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_OperatingLeaseExpense_01a0817f-1eb9-730b-b7f3-c1b6c000ab52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SettlementOfObligationThroughShareIssuance_01a0817f-1eb9-7572-a47f-09b6c5e43c44" xlink:href="tmc-20260930.xsd#tmc_SettlementOfObligationThroughShareIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_SettlementOfObligationThroughShareIssuance_01a0817f-1eb9-7572-a47f-09b6c5e43c44" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GainLossOnRemeasurementOfEquitySettledObligation_01a0817f-1eb9-7be0-a335-3b55bf5d441e" xlink:href="tmc-20260930.xsd#tmc_GainLossOnRemeasurementOfEquitySettledObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_GainLossOnRemeasurementOfEquitySettledObligation_01a0817f-1eb9-7be0-a335-3b55bf5d441e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_01a0817f-1eb9-7a5e-a980-848002f2a19e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_ShareBasedCompensation_01a0817f-1eb9-7a5e-a980-848002f2a19e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_01a0817f-1eb9-73de-b971-c7bc3cff8143" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_EquityMethodInvestmentRealizedGainLossOnDisposal_01a0817f-1eb9-73de-b971-c7bc3cff8143" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GainLossOnDilutionOfInvestments_01a0817f-1eb9-7e0d-8ddc-6a10ea638a3f" xlink:href="tmc-20260930.xsd#tmc_GainLossOnDilutionOfInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_GainLossOnDilutionOfInvestments_01a0817f-1eb9-7e0d-8ddc-6a10ea638a3f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FairValueAdjustmentsOfRoyaltyLiability_01a18cc6-c53d-75c2-9bf3-92455e9dda72" xlink:href="tmc-20260930.xsd#tmc_FairValueAdjustmentsOfRoyaltyLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_FairValueAdjustmentsOfRoyaltyLiability_01a18cc6-c53d-75c2-9bf3-92455e9dda72" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_01a0817f-1eb9-71e0-bd06-a498670b4782" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAdjustmentOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_01a0817f-1eb9-71e0-bd06-a498670b4782" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_01a0817f-1eb9-769e-ae15-207ed8df4a93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_01a0817f-1eb9-769e-ae15-207ed8df4a93" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_InterestPaidOnShortTermBorrowings_01a0817f-1eb9-7d40-a163-e264c2eef9b6" xlink:href="tmc-20260930.xsd#tmc_InterestPaidOnShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_tmc_InterestPaidOnShortTermBorrowings_01a0817f-1eb9-7d40-a163-e264c2eef9b6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a0817f-1eb9-7bae-ada0-536bf6aed85a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ItemsNotAffectingCashAbstract_01a0817f-1eb9-7832-b341-3d4f087a67a3" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a0817f-1eb9-7bae-ada0-536bf6aed85a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_IncreaseDecreaseInReceivablesAndPrepaidExpense_01a0817f-1eb9-70b2-a6ff-ffeee8cefffc" xlink:href="tmc-20260930.xsd#tmc_IncreaseDecreaseInReceivablesAndPrepaidExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a0817f-1eb9-7bae-ada0-536bf6aed85a" xlink:to="loc_tmc_IncreaseDecreaseInReceivablesAndPrepaidExpense_01a0817f-1eb9-70b2-a6ff-ffeee8cefffc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_01a0817f-1eb9-7475-a892-ba38b0ca3787" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_01a0817f-1eb9-7bae-ada0-536bf6aed85a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_01a0817f-1eb9-7475-a892-ba38b0ca3787" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a0817f-1eb9-73eb-b661-0806edabb359" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_01a0817f-1eb9-7b82-a1bf-3793fb1326c3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_01a0817f-1eb9-73eb-b661-0806edabb359" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a0817f-1eb9-7e42-b22c-0253d7547c61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a0817f-1eb9-7e42-b22c-0253d7547c61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_01a0817f-1eb9-7430-a6ff-fec701921ab9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_01a0817f-1eb9-7430-a6ff-fec701921ab9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a0817f-1eb9-7361-a552-54810818cc53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:to="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a0817f-1eb9-7361-a552-54810818cc53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a0817f-1eb9-776f-8924-0ef409f40f63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_01a0817f-1eb9-7cfd-ac72-b092bbf5deaa" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_01a0817f-1eb9-776f-8924-0ef409f40f63" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_01a0817f-1eb9-7f2b-8417-883f5aab6572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfPrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_01a0817f-1eb9-7f2b-8417-883f5aab6572" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ProceedsFromIssuanceRegisteredDirectOffering_01a0817f-1eb9-7818-8b53-d0fb6bc5b815" xlink:href="tmc-20260930.xsd#tmc_ProceedsFromIssuanceRegisteredDirectOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_tmc_ProceedsFromIssuanceRegisteredDirectOffering_01a0817f-1eb9-7818-8b53-d0fb6bc5b815" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PaymentsOfStockIssuanceCostsRegisteredDirectOffering_01a0817f-1eb9-74c2-b2c2-e3cb9af57e6a" xlink:href="tmc-20260930.xsd#tmc_PaymentsOfStockIssuanceCostsRegisteredDirectOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_tmc_PaymentsOfStockIssuanceCostsRegisteredDirectOffering_01a0817f-1eb9-74c2-b2c2-e3cb9af57e6a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_01a0817f-1eb9-7bd3-94f7-d2820df65023" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_01a0817f-1eb9-7bd3-94f7-d2820df65023" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromWarrantExercises_01a0817f-1eb9-7d32-9bc0-a696ec706087" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromWarrantExercises"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_ProceedsFromWarrantExercises_01a0817f-1eb9-7d32-9bc0-a696ec706087" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_01a0817f-1eb9-73a0-a452-05fef5277153" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_01a0817f-1eb9-73a0-a452-05fef5277153" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RepaymentOfWorkingCapitalLoan_01a0817f-1eb9-7192-98db-738dc216fe19" xlink:href="tmc-20260930.xsd#tmc_RepaymentOfWorkingCapitalLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_tmc_RepaymentOfWorkingCapitalLoan_01a0817f-1eb9-7192-98db-738dc216fe19" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_01a0817f-1eb9-7a19-a9e0-af40d90d4107" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_01a0817f-1eb9-7a19-a9e0-af40d90d4107" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockPlans_01a0817f-1eb9-7370-8d64-6d401cb6360e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_ProceedsFromStockPlans_01a0817f-1eb9-7370-8d64-6d401cb6360e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_01a0817f-1eb9-7aef-87f7-ea4af2c3ce27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_01a0817f-1eb9-7706-8c96-14ff39b7f65c" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_01a0817f-1eb9-7aef-87f7-ea4af2c3ce27" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_01a0817f-1eb9-7c0f-883b-d41fdf0a5a91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_01a0817f-1eb9-7c0f-883b-d41fdf0a5a91" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a0817f-1eb9-71de-86ca-ee7cdb7d1636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a0817f-1eb9-71de-86ca-ee7cdb7d1636" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a0817f-1eb9-7d88-9705-312908a6c21a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0817f-1eb9-7a66-8817-faee09e08eee" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a0817f-1eb9-7d88-9705-312908a6c21a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a0817f-1eb9-71ae-aecb-f00fdcd6b65c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/NatureofOperationsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#NatureofOperationsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/NatureofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsIncurredInOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesTable_01a0817f-1eb9-784f-94b8-fa5cd8653bae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsIncurredInOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_us-gaap_CostsIncurredInOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesTable_01a0817f-1eb9-784f-94b8-fa5cd8653bae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a0817f-1eb9-7e97-8a84-567fa32ea50d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CostsIncurredInOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesTable_01a0817f-1eb9-784f-94b8-fa5cd8653bae" xlink:to="loc_dei_LegalEntityAxis_01a0817f-1eb9-7e97-8a84-567fa32ea50d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a0817f-1eb9-7e97-8a84-567fa32ea50d_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a0817f-1eb9-7e97-8a84-567fa32ea50d" xlink:to="loc_dei_EntityDomain_01a0817f-1eb9-7e97-8a84-567fa32ea50d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a0817f-1eb9-72fa-ab6e-a491044f8abe" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a0817f-1eb9-7e97-8a84-567fa32ea50d" xlink:to="loc_dei_EntityDomain_01a0817f-1eb9-72fa-ab6e-a491044f8abe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NationalOceanicAndAtmosphericAdministrationMember_01a1b34c-d932-76c7-8dc4-9170efda3530" xlink:href="tmc-20260930.xsd#tmc_NationalOceanicAndAtmosphericAdministrationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a0817f-1eb9-72fa-ab6e-a491044f8abe" xlink:to="loc_tmc_NationalOceanicAndAtmosphericAdministrationMember_01a1b34c-d932-76c7-8dc4-9170efda3530" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-7b85-b382-b4058b343ad6" xlink:href="tmc-20260930.xsd#tmc_NauruOceanResourcesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a0817f-1eb9-72fa-ab6e-a491044f8abe" xlink:to="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-7b85-b382-b4058b343ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TongaOffshoreMiningLimitedMember_01a0817f-1eb9-7ef0-9c7c-5bfbf7d55c14" xlink:href="tmc-20260930.xsd#tmc_TongaOffshoreMiningLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a0817f-1eb9-72fa-ab6e-a491044f8abe" xlink:to="loc_tmc_TongaOffshoreMiningLimitedMember_01a0817f-1eb9-7ef0-9c7c-5bfbf7d55c14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7cc0-8c02-0cd9d597744e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CostsIncurredInOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesTable_01a0817f-1eb9-784f-94b8-fa5cd8653bae" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7cc0-8c02-0cd9d597744e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7cc0-8c02-0cd9d597744e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7cc0-8c02-0cd9d597744e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7cc0-8c02-0cd9d597744e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7814-9c3b-b3110412e241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7cc0-8c02-0cd9d597744e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7814-9c3b-b3110412e241" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NoriExplorationContractMember_01a0817f-1eb9-7120-8dfb-f72fc23e304e" xlink:href="tmc-20260930.xsd#tmc_NoriExplorationContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7814-9c3b-b3110412e241" xlink:to="loc_tmc_NoriExplorationContractMember_01a0817f-1eb9-7120-8dfb-f72fc23e304e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TongaOffshoreMiningLimitedExplorationContractMember_01a0817f-1eb9-7a70-b208-fea281c9724a" xlink:href="tmc-20260930.xsd#tmc_TongaOffshoreMiningLimitedExplorationContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7814-9c3b-b3110412e241" xlink:to="loc_tmc_TongaOffshoreMiningLimitedExplorationContractMember_01a0817f-1eb9-7a70-b208-fea281c9724a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NumberOfApplicationsPending_01a1b1ba-1ffc-7296-949a-82fb604ca473" xlink:href="tmc-20260930.xsd#tmc_NumberOfApplicationsPending"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_tmc_NumberOfApplicationsPending_01a1b1ba-1ffc-7296-949a-82fb604ca473" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ExplorationAndCommercialRecoveryAreaOfLand_01a0817f-1eb9-740e-a16a-617c049f13bc" xlink:href="tmc-20260930.xsd#tmc_ExplorationAndCommercialRecoveryAreaOfLand"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_tmc_ExplorationAndCommercialRecoveryAreaOfLand_01a0817f-1eb9-740e-a16a-617c049f13bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ExplorationLicenseAppliedAreaOfLand_01a0817f-1eb9-7eda-b245-f847c37d1cfa" xlink:href="tmc-20260930.xsd#tmc_ExplorationLicenseAppliedAreaOfLand"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_tmc_ExplorationLicenseAppliedAreaOfLand_01a0817f-1eb9-7eda-b245-f847c37d1cfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_CommercialRecoveryAreaOfLand_01a0817f-1eb9-745c-9a55-80e0be6f635b" xlink:href="tmc-20260930.xsd#tmc_CommercialRecoveryAreaOfLand"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_tmc_CommercialRecoveryAreaOfLand_01a0817f-1eb9-745c-9a55-80e0be6f635b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNumberOfPlaintiffs_01a1b1c5-242e-7947-af6c-7d15a60530cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyNumberOfPlaintiffs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_us-gaap_LossContingencyNumberOfPlaintiffs_01a1b1c5-242e-7947-af6c-7d15a60530cc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyDamagesSoughtValue_01a1b1c8-8ce8-77a6-9f1c-ed95be64da3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingencyDamagesSoughtValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_us-gaap_LossContingencyDamagesSoughtValue_01a1b1c8-8ce8-77a6-9f1c-ed95be64da3c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FiniteLivedIntangibleAssetContractExtensionPeriod_01a0817f-1eb9-74ee-8250-7fe0e813292c" xlink:href="tmc-20260930.xsd#tmc_FiniteLivedIntangibleAssetContractExtensionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivitiesLineItems_01a0817f-1eb9-7be9-9af9-32c1096b5549" xlink:to="loc_tmc_FiniteLivedIntangibleAssetContractExtensionPeriod_01a0817f-1eb9-74ee-8250-7fe0e813292c" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/StrategicAlliancewithAllseasandAffiliatesNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#StrategicAlliancewithAllseasandAffiliatesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/StrategicAlliancewithAllseasandAffiliatesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:href="tmc-20260930.xsd#tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:href="tmc-20260930.xsd#tmc_StrategicAllianceWithAllseasAndAffiliatesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f5a-bb89-f12765e04f1f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7ccc-9c8a-f74e2cb0cf54" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f5a-bb89-f12765e04f1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AllseasGroupSMember_01a0817f-1eb9-7471-8c39-1c9da714e97d" xlink:href="tmc-20260930.xsd#tmc_AllseasGroupSMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f5a-bb89-f12765e04f1f" xlink:to="loc_tmc_AllseasGroupSMember_01a0817f-1eb9-7471-8c39-1c9da714e97d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AllseasAndAffiliatesMember_01a1a72d-8856-774f-bb0b-2f05d1caa527" xlink:href="tmc-20260930.xsd#tmc_AllseasAndAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f5a-bb89-f12765e04f1f" xlink:to="loc_tmc_AllseasAndAffiliatesMember_01a1a72d-8856-774f-bb0b-2f05d1caa527" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1" xlink:to="loc_us-gaap_RelatedPartyDomain_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a0817f-1eb9-7a65-8e1e-674a0152b704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a0817f-1eb9-7d1c-955f-39c19b5e8fc1" xlink:to="loc_us-gaap_RelatedPartyDomain_01a0817f-1eb9-7a65-8e1e-674a0152b704" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a0817f-1eb9-7b8d-8633-d1e46c60badc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a0817f-1eb9-7a65-8e1e-674a0152b704" xlink:to="loc_us-gaap_RelatedPartyMember_01a0817f-1eb9-7b8d-8633-d1e46c60badc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_01a0817f-1eb9-75e5-a5c7-068859cd26bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_01a0817f-1eb9-75e5-a5c7-068859cd26bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProjectMember_01a0817f-1eb9-75e5-a5c7-068859cd26bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProjectMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_01a0817f-1eb9-75e5-a5c7-068859cd26bb" xlink:to="loc_us-gaap_ProjectMember_01a0817f-1eb9-75e5-a5c7-068859cd26bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProjectMember_01a0817f-1eb9-7948-91e3-f1a610503cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProjectMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_01a0817f-1eb9-75e5-a5c7-068859cd26bb" xlink:to="loc_us-gaap_ProjectMember_01a0817f-1eb9-7948-91e3-f1a610503cc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ProjectManagementTechnologyServicesMember_01a0817f-1eb9-778c-898f-dfba440c9698" xlink:href="tmc-20260930.xsd#tmc_ProjectManagementTechnologyServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProjectMember_01a0817f-1eb9-7948-91e3-f1a610503cc0" xlink:to="loc_tmc_ProjectManagementTechnologyServicesMember_01a0817f-1eb9-778c-898f-dfba440c9698" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a1a72d-8856-7829-82d4-d3810aa5858b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_us-gaap_CreditFacilityAxis_01a1a72d-8856-7829-82d4-d3810aa5858b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a1a72d-8856-7829-82d4-d3810aa5858b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a1a72d-8856-7829-82d4-d3810aa5858b" xlink:to="loc_us-gaap_CreditFacilityDomain_01a1a72d-8856-7829-82d4-d3810aa5858b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a1a72d-8856-77b7-9cc6-48650240b775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a1a72d-8856-7829-82d4-d3810aa5858b" xlink:to="loc_us-gaap_CreditFacilityDomain_01a1a72d-8856-77b7-9cc6-48650240b775" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a1a72d-8856-7556-9029-27f6084ed9e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a1a72d-8856-77b7-9cc6-48650240b775" xlink:to="loc_us-gaap_LineOfCreditMember_01a1a72d-8856-7556-9029-27f6084ed9e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a159da-d68f-775b-9d2c-62a0cd75d7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a159da-d68f-775b-9d2c-62a0cd75d7b6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a159da-d68f-775b-9d2c-62a0cd75d7b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a159da-d68f-775b-9d2c-62a0cd75d7b6" xlink:to="loc_us-gaap_EquityComponentDomain_01a159da-d68f-775b-9d2c-62a0cd75d7b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a159da-d68f-7776-ba49-acd2f66cb03d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a159da-d68f-775b-9d2c-62a0cd75d7b6" xlink:to="loc_us-gaap_EquityComponentDomain_01a159da-d68f-7776-ba49-acd2f66cb03d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a159da-d68f-7777-9afd-4788441f36fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a159da-d68f-7776-ba49-acd2f66cb03d" xlink:to="loc_us-gaap_CommonStockMember_01a159da-d68f-7777-9afd-4788441f36fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a16584-1c7d-74e3-8d57-648a8d539de6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesTable_01a0817f-1eb9-7e34-9903-a9902ade268f" xlink:to="loc_dei_LegalEntityAxis_01a16584-1c7d-74e3-8d57-648a8d539de6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a16584-1c7d-74e3-8d57-648a8d539de6_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a16584-1c7d-74e3-8d57-648a8d539de6" xlink:to="loc_dei_EntityDomain_01a16584-1c7d-74e3-8d57-648a8d539de6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a16584-1c7d-7d04-a187-2b617db5e2e7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a16584-1c7d-74e3-8d57-648a8d539de6" xlink:to="loc_dei_EntityDomain_01a16584-1c7d-7d04-a187-2b617db5e2e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AllseasDeepseaMarineContractorsAndAffiliatesMember_01a16584-c015-7335-9cb0-0ae8582532c9" xlink:href="tmc-20260930.xsd#tmc_AllseasDeepseaMarineContractorsAndAffiliatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a16584-1c7d-7d04-a187-2b617db5e2e7" xlink:to="loc_tmc_AllseasDeepseaMarineContractorsAndAffiliatesMember_01a16584-c015-7335-9cb0-0ae8582532c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PercentageOfEngineeringProjectManagementAndVesselUseServicesCostsIncurredToBeSettledThroughShareIssuance_01a0817f-1eb9-7bac-a38b-cb9056d304b1" xlink:href="tmc-20260930.xsd#tmc_PercentageOfEngineeringProjectManagementAndVesselUseServicesCostsIncurredToBeSettledThroughShareIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_PercentageOfEngineeringProjectManagementAndVesselUseServicesCostsIncurredToBeSettledThroughShareIssuance_01a0817f-1eb9-7bac-a38b-cb9056d304b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PercentageOfAdditionalNegotiatedCostsToBeSettledThroughShareIssuance_01a0817f-1eb9-7658-bd83-3b98653e1ba6" xlink:href="tmc-20260930.xsd#tmc_PercentageOfAdditionalNegotiatedCostsToBeSettledThroughShareIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_PercentageOfAdditionalNegotiatedCostsToBeSettledThroughShareIssuance_01a0817f-1eb9-7658-bd83-3b98653e1ba6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PercentageOfRepayableThroughProductionBasedRepaymentMechanism_01a1a719-4d1c-7fbe-bcae-e7a2491d8cc2" xlink:href="tmc-20260930.xsd#tmc_PercentageOfRepayableThroughProductionBasedRepaymentMechanism"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_PercentageOfRepayableThroughProductionBasedRepaymentMechanism_01a1a719-4d1c-7fbe-bcae-e7a2491d8cc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquitySettledObligationSharePriceDiscount_01a0817f-1eb9-74bb-baa4-f472ed2b486f" xlink:href="tmc-20260930.xsd#tmc_EquitySettledObligationSharePriceDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_EquitySettledObligationSharePriceDiscount_01a0817f-1eb9-74bb-baa4-f472ed2b486f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquitySettledObligationThresholdNumberOfTradingDays_01a0817f-1eb9-7312-be9c-e502783d14ad" xlink:href="tmc-20260930.xsd#tmc_EquitySettledObligationThresholdNumberOfTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_EquitySettledObligationThresholdNumberOfTradingDays_01a0817f-1eb9-7312-be9c-e502783d14ad" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GainLossOnRemeasurementOfEquitySettledObligation_01a0817f-1eb9-700b-a4b8-28a1629c00f7" xlink:href="tmc-20260930.xsd#tmc_GainLossOnRemeasurementOfEquitySettledObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_GainLossOnRemeasurementOfEquitySettledObligation_01a0817f-1eb9-700b-a4b8-28a1629c00f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DeferredLiabilityCharges_01a1ca75-12d2-7829-942d-cc2080855957" xlink:href="tmc-20260930.xsd#tmc_DeferredLiabilityCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_DeferredLiabilityCharges_01a1ca75-12d2-7829-942d-cc2080855957" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DeferredCostsIncurred_01a1ca76-6fee-7fce-ab09-ed4dec842904" xlink:href="tmc-20260930.xsd#tmc_DeferredCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_DeferredCostsIncurred_01a1ca76-6fee-7fce-ab09-ed4dec842904" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AdditionalNegotiatedCostsIncurred_01a1ca77-956a-72d5-9a8c-ce498f09edc9" xlink:href="tmc-20260930.xsd#tmc_AdditionalNegotiatedCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_AdditionalNegotiatedCostsIncurred_01a1ca77-956a-72d5-9a8c-ce498f09edc9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a0817f-1eb9-7a7f-ba39-3e2c83a606f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a0817f-1eb9-7a7f-ba39-3e2c83a606f2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RelatedPartyReimbursementForEligibleCostsCashPaymentLimitPercentage_01a1a715-fbae-73bc-98d4-b4efd14e4f2a" xlink:href="tmc-20260930.xsd#tmc_RelatedPartyReimbursementForEligibleCostsCashPaymentLimitPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_RelatedPartyReimbursementForEligibleCostsCashPaymentLimitPercentage_01a1a715-fbae-73bc-98d4-b4efd14e4f2a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_CommercialProductionAgreementContractTerm_01a0817f-1eb9-76e6-896b-d01e69c52334" xlink:href="tmc-20260930.xsd#tmc_CommercialProductionAgreementContractTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_CommercialProductionAgreementContractTerm_01a0817f-1eb9-76e6-896b-d01e69c52334" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExplorationExpense_01a0817f-1eb9-79e9-b58a-60a3b89b09cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExplorationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_ExplorationExpense_01a0817f-1eb9-79e9-b58a-60a3b89b09cf" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_01a159d7-32ff-7c2a-bd45-ed9273ab4dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_OperatingLeaseExpense_01a159d7-32ff-7c2a-bd45-ed9273ab4dbf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a159da-d68f-7a2c-a0d9-2f93be95d1b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a159da-d68f-7a2c-a0d9-2f93be95d1b5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a159da-d68f-7beb-87c5-176577fdcda1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a159da-d68f-7beb-87c5-176577fdcda1" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_01a159da-d68f-7344-9358-62810deda103" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_01a159da-d68f-7344-9358-62810deda103" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_InvestmentOwnedCommonSharesOutstandingPercentage_01a159da-d68f-7b10-a631-74049ec1bad7" xlink:href="tmc-20260930.xsd#tmc_InvestmentOwnedCommonSharesOutstandingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_StrategicAllianceWithAllseasAndAffiliatesLineItems_01a0817f-1eb9-7f50-a235-19674b3865b8" xlink:to="loc_tmc_InvestmentOwnedCommonSharesOutstandingPercentage_01a159da-d68f-7b10-a631-74049ec1bad7" xlink:type="arc" order="17"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/InvestmentsScheduleofInvestmentsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#InvestmentsScheduleofInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/InvestmentsScheduleofInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-74a1-928b-b9ec9fbaf286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-771a-8723-719de8ae5d97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-74a1-928b-b9ec9fbaf286" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-771a-8723-719de8ae5d97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-7f80-9d38-890b397de108" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-771a-8723-719de8ae5d97" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-7f80-9d38-890b397de108" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-7f80-9d38-890b397de108_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-7f80-9d38-890b397de108" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-7f80-9d38-890b397de108_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-77cf-900f-a9e21b9a5821" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-7f80-9d38-890b397de108" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-77cf-900f-a9e21b9a5821" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_MetalsRoyaltyCompanyMember_01a0817f-1eb9-7e20-aed3-e8e4f6644758" xlink:href="tmc-20260930.xsd#tmc_MetalsRoyaltyCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-77cf-900f-a9e21b9a5821" xlink:to="loc_tmc_MetalsRoyaltyCompanyMember_01a0817f-1eb9-7e20-aed3-e8e4f6644758" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquityMethodInvestment1554997B.c.LtdMember_01a0817f-1eb9-7707-875b-899e632404ce" xlink:href="tmc-20260930.xsd#tmc_EquityMethodInvestment1554997B.c.LtdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-77cf-900f-a9e21b9a5821" xlink:to="loc_tmc_EquityMethodInvestment1554997B.c.LtdMember_01a0817f-1eb9-7707-875b-899e632404ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:href="tmc-20260930.xsd#tmc_LongTermInvestmentsRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-74a1-928b-b9ec9fbaf286" xlink:to="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_01a0817f-1eb9-741c-b90d-5e9ba7a903f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_us-gaap_LongTermInvestments_01a0817f-1eb9-741c-b90d-5e9ba7a903f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquityMethodInvestmentTransferOfInvestmentFromOneEntityToAnother_01a0817f-1eb9-7718-a386-471adc9c40fa" xlink:href="tmc-20260930.xsd#tmc_EquityMethodInvestmentTransferOfInvestmentFromOneEntityToAnother"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_tmc_EquityMethodInvestmentTransferOfInvestmentFromOneEntityToAnother_01a0817f-1eb9-7718-a386-471adc9c40fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a0817f-1eb9-7eb0-a7a5-e1bd2badbe1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a0817f-1eb9-7eb0-a7a5-e1bd2badbe1d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GainLossOnDilutionOfInvestments_01a0817f-1eb9-7fc0-a7b5-33af1dc3a172" xlink:href="tmc-20260930.xsd#tmc_GainLossOnDilutionOfInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_tmc_GainLossOnDilutionOfInvestments_01a0817f-1eb9-7fc0-a7b5-33af1dc3a172" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a0817f-1eb9-7138-9a9e-bdfcc2692152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a0817f-1eb9-7138-9a9e-bdfcc2692152" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a0817f-1eb9-773f-b345-f073ba131d28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_LongTermInvestmentsRollForward_01a1a759-3ecd-7c04-87af-1e390d872456" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a0817f-1eb9-773f-b345-f073ba131d28" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_01a0817f-1eb9-7e5e-8fce-c84c7031fbc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermInvestments"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/InvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a15f47-1172-71b2-bcb7-e57920f86291" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:to="loc_dei_LegalEntityAxis_01a15f47-1172-71b2-bcb7-e57920f86291" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a15f47-1172-71b2-bcb7-e57920f86291_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a15f47-1172-71b2-bcb7-e57920f86291" xlink:to="loc_dei_EntityDomain_01a15f47-1172-71b2-bcb7-e57920f86291_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a15f47-1172-789f-9ad0-5778dfb6882a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a15f47-1172-71b2-bcb7-e57920f86291" xlink:to="loc_dei_EntityDomain_01a15f47-1172-789f-9ad0-5778dfb6882a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_MetalsRoyaltyCompanyMember_01a15f47-1172-7b84-b5c3-493332750fe8" xlink:href="tmc-20260930.xsd#tmc_MetalsRoyaltyCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a15f47-1172-789f-9ad0-5778dfb6882a" xlink:to="loc_tmc_MetalsRoyaltyCompanyMember_01a15f47-1172-7b84-b5c3-493332750fe8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a1a793-342b-78c2-8422-38d5d90c2e75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a1a793-342b-78c2-8422-38d5d90c2e75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-78c2-8422-38d5d90c2e75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a1a793-342b-78c2-8422-38d5d90c2e75" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-78c2-8422-38d5d90c2e75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-782b-9585-7e8c17b99042" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a1a793-342b-78c2-8422-38d5d90c2e75" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-782b-9585-7e8c17b99042" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_01a1a794-08df-7b0a-b07d-42b839d35ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-782b-9585-7e8c17b99042" xlink:to="loc_us-gaap_ConvertibleDebtMember_01a1a794-08df-7b0a-b07d-42b839d35ab1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_01a1b1da-5c87-796a-8d36-77c5e37a1e29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a1a793-342b-782b-9585-7e8c17b99042" xlink:to="loc_us-gaap_SecuredDebtMember_01a1b1da-5c87-796a-8d36-77c5e37a1e29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a15f48-3881-7780-9bfa-b50c0e166fa2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a15f48-3881-7780-9bfa-b50c0e166fa2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7780-9bfa-b50c0e166fa2_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a15f48-3881-7780-9bfa-b50c0e166fa2" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7780-9bfa-b50c0e166fa2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7c43-a3b0-d5bb6254d3e4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a15f48-3881-7780-9bfa-b50c0e166fa2" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7c43-a3b0-d5bb6254d3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_MetalsRoyaltyCompanyMember_01a15f49-7595-71cc-96b5-15a0ad31def5" xlink:href="tmc-20260930.xsd#tmc_MetalsRoyaltyCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7c43-a3b0-d5bb6254d3e4" xlink:to="loc_tmc_MetalsRoyaltyCompanyMember_01a15f49-7595-71cc-96b5-15a0ad31def5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquityMethodInvestment1554997B.c.LtdMember_01a15f4d-8ee1-7ff9-b61c-bb29eedbca54" xlink:href="tmc-20260930.xsd#tmc_EquityMethodInvestment1554997B.c.LtdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a15f48-3881-7c43-a3b0-d5bb6254d3e4" xlink:to="loc_tmc_EquityMethodInvestment1554997B.c.LtdMember_01a15f4d-8ee1-7ff9-b61c-bb29eedbca54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a15f4c-3eba-7d7c-98ff-39a21744bc8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:to="loc_us-gaap_AwardTypeAxis_01a15f4c-3eba-7d7c-98ff-39a21744bc8b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7d7c-98ff-39a21744bc8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a15f4c-3eba-7d7c-98ff-39a21744bc8b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7d7c-98ff-39a21744bc8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7e12-b744-4f0baccf757e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a15f4c-3eba-7d7c-98ff-39a21744bc8b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7e12-b744-4f0baccf757e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a15f4c-3eba-784f-a835-5683e37066b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7e12-b744-4f0baccf757e" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a15f4c-3eba-784f-a835-5683e37066b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a15f4c-3eba-768a-ba24-aacdce7d51c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15f4c-3eba-7e12-b744-4f0baccf757e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a15f4c-3eba-768a-ba24-aacdce7d51c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_01a1b1d6-fba4-74f2-9761-36e1ef041118" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a0817f-1eb9-78dd-b45b-198445cb882a" xlink:to="loc_srt_StatementScenarioAxis_01a1b1d6-fba4-74f2-9761-36e1ef041118" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1b1d6-fba4-74f2-9761-36e1ef041118_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_01a1b1d6-fba4-74f2-9761-36e1ef041118" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1b1d6-fba4-74f2-9761-36e1ef041118_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1b1d6-fba4-7965-90e3-23fbb8ad47b0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_01a1b1d6-fba4-74f2-9761-36e1ef041118" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1b1d6-fba4-7965-90e3-23fbb8ad47b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_01a1b1d7-27c4-7f74-b83a-146566bdad7b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_01a1b1d6-fba4-7965-90e3-23fbb8ad47b0" xlink:to="loc_srt_ScenarioForecastMember_01a1b1d7-27c4-7f74-b83a-146566bdad7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PercentageOfContributionToGrossRoyalty_01a15f46-77cf-7aac-9698-2ddf786a359e" xlink:href="tmc-20260930.xsd#tmc_PercentageOfContributionToGrossRoyalty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_PercentageOfContributionToGrossRoyalty_01a15f46-77cf-7aac-9698-2ddf786a359e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ContingentValueRightsIssued_01a15f46-77cf-7fc9-b9e7-acbe368d5078" xlink:href="tmc-20260930.xsd#tmc_ContingentValueRightsIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_ContingentValueRightsIssued_01a15f46-77cf-7fc9-b9e7-acbe368d5078" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GrossOverridingProductionRoyaltyInterestPercentage_01a15f47-1172-7060-94b7-cfa9ebed9504" xlink:href="tmc-20260930.xsd#tmc_GrossOverridingProductionRoyaltyInterestPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_GrossOverridingProductionRoyaltyInterestPercentage_01a15f47-1172-7060-94b7-cfa9ebed9504" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AdditionalRoyaltyInterestPercentage_01a15f47-1172-71d8-b0e8-94db1e5f3328" xlink:href="tmc-20260930.xsd#tmc_AdditionalRoyaltyInterestPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_AdditionalRoyaltyInterestPercentage_01a15f47-1172-71d8-b0e8-94db1e5f3328" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyAcquisitionConsiderationTransferred_01a15f47-1172-736f-8579-5efee89903a6" xlink:href="tmc-20260930.xsd#tmc_RoyaltyAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_RoyaltyAcquisitionConsiderationTransferred_01a15f47-1172-736f-8579-5efee89903a6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyAcquisitionConsiderationTransferredCash_01a15f47-1172-7e5c-83e6-092a2e198e3c" xlink:href="tmc-20260930.xsd#tmc_RoyaltyAcquisitionConsiderationTransferredCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_RoyaltyAcquisitionConsiderationTransferredCash_01a15f47-1172-7e5c-83e6-092a2e198e3c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyAcquisitionConsiderationTransferredShares_01a15f47-1172-7ce6-98dc-96e31dbad4d8" xlink:href="tmc-20260930.xsd#tmc_RoyaltyAcquisitionConsiderationTransferredShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_RoyaltyAcquisitionConsiderationTransferredShares_01a15f47-1172-7ce6-98dc-96e31dbad4d8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyAcquisitionRoyaltyInterestAcquiredPercentage_01a1b1d4-118b-73dc-8cea-0e903c6581ff" xlink:href="tmc-20260930.xsd#tmc_RoyaltyAcquisitionRoyaltyInterestAcquiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_RoyaltyAcquisitionRoyaltyInterestAcquiredPercentage_01a1b1d4-118b-73dc-8cea-0e903c6581ff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyAcquisitionSharePrice_01a1a790-22ef-7153-bf52-8f622863d522" xlink:href="tmc-20260930.xsd#tmc_RoyaltyAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_RoyaltyAcquisitionSharePrice_01a1a790-22ef-7153-bf52-8f622863d522" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a1b1d7-fc3e-7980-a74d-ab1d10d46547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a1b1d7-fc3e-7980-a74d-ab1d10d46547" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockIssuedDuringPeriodSharesFinancingCompensationAndRoyaltyTransactions_01a15f48-3881-7943-a353-79ba3d835219" xlink:href="tmc-20260930.xsd#tmc_StockIssuedDuringPeriodSharesFinancingCompensationAndRoyaltyTransactions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_StockIssuedDuringPeriodSharesFinancingCompensationAndRoyaltyTransactions_01a15f48-3881-7943-a353-79ba3d835219" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NumberOfSharesAcquiredInInvestment_01a15f48-3881-7511-b7b7-00b1386ccbe8" xlink:href="tmc-20260930.xsd#tmc_NumberOfSharesAcquiredInInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_NumberOfSharesAcquiredInInvestment_01a15f48-3881-7511-b7b7-00b1386ccbe8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ValueOfSharesAcquiredInInvestment_01a15f48-3881-79b9-bed5-f5765545ba4c" xlink:href="tmc-20260930.xsd#tmc_ValueOfSharesAcquiredInInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_ValueOfSharesAcquiredInInvestment_01a15f48-3881-79b9-bed5-f5765545ba4c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GainLossOnDilutionOfInvestments_01a15f48-3881-7b0e-9e45-f8008376e0e9" xlink:href="tmc-20260930.xsd#tmc_GainLossOnDilutionOfInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_GainLossOnDilutionOfInvestments_01a15f48-3881-7b0e-9e45-f8008376e0e9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a15f48-3881-7ecf-a952-f667399aaf97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a15f48-3881-7ecf-a952-f667399aaf97" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a15f49-7595-795b-97de-32b530b06085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a15f49-7595-795b-97de-32b530b06085" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DebtConversionConvertedInstrumentSharesIssuableUponConversion_01a15f46-77cf-7f07-a4d9-1287c1b81b1a" xlink:href="tmc-20260930.xsd#tmc_DebtConversionConvertedInstrumentSharesIssuableUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_DebtConversionConvertedInstrumentSharesIssuableUponConversion_01a15f46-77cf-7f07-a4d9-1287c1b81b1a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a1a7af-757b-70a2-9b5d-ce5209b4af72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a1a7af-757b-70a2-9b5d-ce5209b4af72" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a15f4c-3eba-7d00-94b3-0f42ba93257c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a15f4c-3eba-7d00-94b3-0f42ba93257c" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a15f4c-3eba-7426-a85b-071f33e02823" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a15f4c-3eba-7426-a85b-071f33e02823" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EquityMethodInvestmentCarryingValueThresholdPercentage_01a1cef5-6a03-7527-b054-def8b6fd0392" xlink:href="tmc-20260930.xsd#tmc_EquityMethodInvestmentCarryingValueThresholdPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_EquityMethodInvestmentCarryingValueThresholdPercentage_01a1cef5-6a03-7527-b054-def8b6fd0392" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ProceedsFromEquityMethodInvestmentDistributionReturnOfCapitalPerShare_01a15f4d-f6ea-7f17-9e93-808fbbf31952" xlink:href="tmc-20260930.xsd#tmc_ProceedsFromEquityMethodInvestmentDistributionReturnOfCapitalPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_tmc_ProceedsFromEquityMethodInvestmentDistributionReturnOfCapitalPerShare_01a15f4d-f6ea-7f17-9e93-808fbbf31952" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a15f4d-f6ea-7936-8582-fbfbe53deed5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a0817f-1eb9-7784-b1c9-76e349dff06f" xlink:to="loc_us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_01a15f4d-f6ea-7936-8582-fbfbe53deed5" xlink:type="arc" order="22"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/RoyaltyLiabilityNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#RoyaltyLiabilityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/RoyaltyLiabilityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyLiabilityLineItems_01a0817f-1eb9-7915-8dfc-a1476319159a" xlink:href="tmc-20260930.xsd#tmc_RoyaltyLiabilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:href="tmc-20260930.xsd#tmc_RoyaltyLiabilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_tmc_RoyaltyLiabilityLineItems_01a0817f-1eb9-7915-8dfc-a1476319159a" xlink:to="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7884-b4be-47b0ebd19c13" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:to="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7884-b4be-47b0ebd19c13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7884-b4be-47b0ebd19c13_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7884-b4be-47b0ebd19c13" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7884-b4be-47b0ebd19c13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f58-b1ef-346dd4d2636e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7884-b4be-47b0ebd19c13" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f58-b1ef-346dd4d2636e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-78e5-a0ee-4b8313d6ea69" xlink:href="tmc-20260930.xsd#tmc_NauruOceanResourcesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7f58-b1ef-346dd4d2636e" xlink:to="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-78e5-a0ee-4b8313d6ea69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-709a-815f-fd2ea8a5e77c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-709a-815f-fd2ea8a5e77c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-709a-815f-fd2ea8a5e77c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-709a-815f-fd2ea8a5e77c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-709a-815f-fd2ea8a5e77c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-7cc3-980b-94afb8c76a5c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a0817f-1eb9-709a-815f-fd2ea8a5e77c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-7cc3-980b-94afb8c76a5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_LowCarbonRoyaltiesMember_01a0817f-1eb9-71a3-870c-f7333166dfb1" xlink:href="tmc-20260930.xsd#tmc_LowCarbonRoyaltiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a0817f-1eb9-7cc3-980b-94afb8c76a5c" xlink:to="loc_tmc_LowCarbonRoyaltiesMember_01a0817f-1eb9-71a3-870c-f7333166dfb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_01a1cc0f-570c-7050-87c8-e2d1ff358340" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_01a1cc0f-570c-7050-87c8-e2d1ff358340" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a1cc0f-570c-7050-87c8-e2d1ff358340_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a1cc0f-570c-7050-87c8-e2d1ff358340" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a1cc0f-570c-7050-87c8-e2d1ff358340_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a1cc0f-570c-788d-bfea-f91bd2f3febb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a1cc0f-570c-7050-87c8-e2d1ff358340" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a1cc0f-570c-788d-bfea-f91bd2f3febb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_01a1cc0f-6f58-7c8a-9920-3e098fcbb479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a1cc0f-570c-788d-bfea-f91bd2f3febb" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_01a1cc0f-6f58-7c8a-9920-3e098fcbb479" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_01a1cc0f-b180-7f5d-8e46-53cfb233ae87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:to="loc_us-gaap_ValuationTechniqueAxis_01a1cc0f-b180-7f5d-8e46-53cfb233ae87" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_01a1cc0f-b180-7f5d-8e46-53cfb233ae87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_01a1cc0f-b180-7f5d-8e46-53cfb233ae87" xlink:to="loc_us-gaap_ValuationTechniqueDomain_01a1cc0f-b180-7f5d-8e46-53cfb233ae87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_01a1cc0f-b180-781a-b062-0551d48c8d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_01a1cc0f-b180-7f5d-8e46-53cfb233ae87" xlink:to="loc_us-gaap_ValuationTechniqueDomain_01a1cc0f-b180-781a-b062-0551d48c8d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeApproachValuationTechniqueMember_01a1cc10-1cdc-707e-ad60-1f94e951c17f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeApproachValuationTechniqueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_01a1cc0f-b180-781a-b062-0551d48c8d1d" xlink:to="loc_us-gaap_IncomeApproachValuationTechniqueMember_01a1cc10-1cdc-707e-ad60-1f94e951c17f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_RoyaltyLiabilityTable_01a0817f-1eb9-7d55-960f-e1cf9050c729" xlink:to="loc_srt_RangeAxis_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13" xlink:to="loc_srt_RangeMember_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1cc12-6b09-7aeb-a946-df62fd8de001" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a1cc12-6b09-7ce2-b246-2a50f4cb3f13" xlink:to="loc_srt_RangeMember_01a1cc12-6b09-7aeb-a946-df62fd8de001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a1cc12-886c-7657-b2bb-166a105bdfed" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1cc12-6b09-7aeb-a946-df62fd8de001" xlink:to="loc_srt_MinimumMember_01a1cc12-886c-7657-b2bb-166a105bdfed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1cc12-9f90-7f72-9262-a5bbc88f5bdf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1cc12-6b09-7aeb-a946-df62fd8de001" xlink:to="loc_srt_MaximumMember_01a1cc12-9f90-7f72-9262-a5bbc88f5bdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyLiabilityForZonesAToCFairValue_01a0817f-1eb9-790f-a3b5-55b63553bfb9" xlink:href="tmc-20260930.xsd#tmc_RoyaltyLiabilityForZonesAToCFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_RoyaltyLiabilityLineItems_01a0817f-1eb9-7915-8dfc-a1476319159a" xlink:to="loc_tmc_RoyaltyLiabilityForZonesAToCFairValue_01a0817f-1eb9-790f-a3b5-55b63553bfb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyLiabilityMeasurementInput_01a1cc0f-2b71-7c1a-aac0-f0046b0dee1f" xlink:href="tmc-20260930.xsd#tmc_RoyaltyLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_RoyaltyLiabilityLineItems_01a0817f-1eb9-7915-8dfc-a1476319159a" xlink:to="loc_tmc_RoyaltyLiabilityMeasurementInput_01a1cc0f-2b71-7c1a-aac0-f0046b0dee1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RoyaltyLiabilityForZoneDFairValue_01a0817f-1eb9-7e49-b168-89c32daca2d9" xlink:href="tmc-20260930.xsd#tmc_RoyaltyLiabilityForZoneDFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_RoyaltyLiabilityLineItems_01a0817f-1eb9-7915-8dfc-a1476319159a" xlink:to="loc_tmc_RoyaltyLiabilityForZoneDFairValue_01a0817f-1eb9-7e49-b168-89c32daca2d9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ExplorationandEvaluationExpensesDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ExplorationandEvaluationExpensesDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ExplorationandEvaluationExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:href="tmc-20260930.xsd#tmc_ExplorationAndEvaluationExpensesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ExplorationAndEvaluationExpensesTable_01a1b1ec-cab9-75c2-a8bc-4f4965bc6c62" xlink:href="tmc-20260930.xsd#tmc_ExplorationAndEvaluationExpensesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_ExplorationAndEvaluationExpensesTable_01a1b1ec-cab9-75c2-a8bc-4f4965bc6c62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1ed-33f0-7e34-be57-eaf831f4d338" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesTable_01a1b1ec-cab9-75c2-a8bc-4f4965bc6c62" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1ed-33f0-7e34-be57-eaf831f4d338" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1b1ed-33f0-7e34-be57-eaf831f4d338_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1ed-33f0-7e34-be57-eaf831f4d338" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1b1ed-33f0-7e34-be57-eaf831f4d338_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1b1ed-33f0-77a0-91f4-a20e95d8ca97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1ed-33f0-7e34-be57-eaf831f4d338" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1b1ed-33f0-77a0-91f4-a20e95d8ca97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a1b1ed-33f0-7101-bbea-d349b4491d36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a1b1ed-33f0-77a0-91f4-a20e95d8ca97" xlink:to="loc_us-gaap_RelatedPartyMember_01a1b1ed-33f0-7101-bbea-d349b4491d36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EnvironmentalStudies_01a0817f-1eb9-763c-9296-f8bdd205de90" xlink:href="tmc-20260930.xsd#tmc_EnvironmentalStudies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_EnvironmentalStudies_01a0817f-1eb9-763c-9296-f8bdd205de90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ExplorationLabor_01a0817f-1eb9-7fff-a3da-9629c921665e" xlink:href="tmc-20260930.xsd#tmc_ExplorationLabor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_ExplorationLabor_01a0817f-1eb9-7fff-a3da-9629c921665e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_CommonSharesOptionsBasedPayments_01a0817f-1eb9-74fb-b634-0a62eadb96dd" xlink:href="tmc-20260930.xsd#tmc_CommonSharesOptionsBasedPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_CommonSharesOptionsBasedPayments_01a0817f-1eb9-74fb-b634-0a62eadb96dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_MiningTechnologicalAndProcessDevelopment_01a0817f-1eb9-7a3f-9b4b-a29a3973c2c6" xlink:href="tmc-20260930.xsd#tmc_MiningTechnologicalAndProcessDevelopment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_MiningTechnologicalAndProcessDevelopment_01a0817f-1eb9-7a3f-9b4b-a29a3973c2c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FeasibilityAndPrefeasibilityStudies_01a0817f-1eb9-7597-84b6-267eda687198" xlink:href="tmc-20260930.xsd#tmc_FeasibilityAndPrefeasibilityStudies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_FeasibilityAndPrefeasibilityStudies_01a0817f-1eb9-7597-84b6-267eda687198" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SponsorshipTrainingAndStakeholderEngagement_01a0817f-1eb9-77a1-b233-8c824f52e972" xlink:href="tmc-20260930.xsd#tmc_SponsorshipTrainingAndStakeholderEngagement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_SponsorshipTrainingAndStakeholderEngagement_01a0817f-1eb9-77a1-b233-8c824f52e972" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_OtherExplorationAndEvaluationExpenses_01a0817f-1eb9-7d1e-bfed-d94f36b7380b" xlink:href="tmc-20260930.xsd#tmc_OtherExplorationAndEvaluationExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_OtherExplorationAndEvaluationExpenses_01a0817f-1eb9-7d1e-bfed-d94f36b7380b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExplorationExpense_01a0817f-1eb9-7105-a3ca-d4044ae8dedb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExplorationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_us-gaap_ExplorationExpense_01a0817f-1eb9-7105-a3ca-d4044ae8dedb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DeferredCostsIncurred_01a0817f-1eb9-79f6-9781-e4f41111676b" xlink:href="tmc-20260930.xsd#tmc_DeferredCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_DeferredCostsIncurred_01a0817f-1eb9-79f6-9781-e4f41111676b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AdditionalNegotiatedCostsIncurred_01a0817f-1eb9-7b45-aa9d-4eb67a79def6" xlink:href="tmc-20260930.xsd#tmc_AdditionalNegotiatedCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ExplorationAndEvaluationExpensesLineItems_01a1b1ec-cab9-7906-852f-3720b153a674" xlink:to="loc_tmc_AdditionalNegotiatedCostsIncurred_01a0817f-1eb9-7b45-aa9d-4eb67a79def6" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/GeneralandAdministrativeExpensesDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#GeneralandAdministrativeExpensesDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/GeneralandAdministrativeExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:href="tmc-20260930.xsd#tmc_GeneralAndAdministrativeExpenseLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GeneralAndAdministrativeExpenseTable_01a0817f-1eb9-7ad0-b9bf-3dbcbfa4d730" xlink:href="tmc-20260930.xsd#tmc_GeneralAndAdministrativeExpenseTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_tmc_GeneralAndAdministrativeExpenseTable_01a0817f-1eb9-7ad0-b9bf-3dbcbfa4d730" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7d78-b542-130547b2e87f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseTable_01a0817f-1eb9-7ad0-b9bf-3dbcbfa4d730" xlink:to="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7d78-b542-130547b2e87f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7d78-b542-130547b2e87f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7d78-b542-130547b2e87f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7d78-b542-130547b2e87f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-774d-b23c-5128923beb03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7d78-b542-130547b2e87f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-774d-b23c-5128923beb03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7876-b669-a82d4464d71d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-774d-b23c-5128923beb03" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7876-b669-a82d4464d71d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_StockOptionsAndRestrictedStockUnitsMember_01a1a69f-a263-722f-94ca-f17335b084b5" xlink:href="tmc-20260930.xsd#tmc_StockOptionsAndRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-774d-b23c-5128923beb03" xlink:to="loc_tmc_StockOptionsAndRestrictedStockUnitsMember_01a1a69f-a263-722f-94ca-f17335b084b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_01a0817f-1eb9-72e2-8f58-11a37d2c1fd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_ProfessionalFees_01a0817f-1eb9-72e2-8f58-11a37d2c1fd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_InvestorRelationsExpense_01a0817f-1eb9-75da-8e48-2dd78ebb67dc" xlink:href="tmc-20260930.xsd#tmc_InvestorRelationsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_tmc_InvestorRelationsExpense_01a0817f-1eb9-75da-8e48-2dd78ebb67dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_OfficeAndSundryExpenses_01a0817f-1eb9-72c4-a1d6-729f53379c66" xlink:href="tmc-20260930.xsd#tmc_OfficeAndSundryExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_tmc_OfficeAndSundryExpenses_01a0817f-1eb9-72c4-a1d6-729f53379c66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_01a0817f-1eb9-7d41-816a-115c125f5b71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_LaborAndRelatedExpense_01a0817f-1eb9-7d41-816a-115c125f5b71" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseDirectorsFees_01a0817f-1eb9-7283-81fe-bf3cf2dca076" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpenseDirectorsFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_NoninterestExpenseDirectorsFees_01a0817f-1eb9-7283-81fe-bf3cf2dca076" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a0817f-1eb9-785f-a551-ff4ea0144f48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a0817f-1eb9-785f-a551-ff4ea0144f48" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseTransferAgentAndCustodianFees_01a0817f-1eb9-764f-862e-12c4f705c80f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpenseTransferAgentAndCustodianFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_NoninterestExpenseTransferAgentAndCustodianFees_01a0817f-1eb9-764f-862e-12c4f705c80f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TravelAndOtherExpenses_01a0817f-1eb9-7bc3-93f2-a1220592fd5f" xlink:href="tmc-20260930.xsd#tmc_TravelAndOtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_tmc_TravelAndOtherExpenses_01a0817f-1eb9-7bc3-93f2-a1220592fd5f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_01a0817f-1eb9-7d3c-bbf7-c8197c28716c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_01a0817f-1eb9-7d3c-bbf7-c8197c28716c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForSettlementOfProfessionalAndConsultingFees_01a0817f-1eb9-7fa8-83c4-739f0671effc" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForSettlementOfProfessionalAndConsultingFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForSettlementOfProfessionalAndConsultingFees_01a0817f-1eb9-7fa8-83c4-739f0671effc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a1a6a4-0f53-7d68-910a-d324cf9d07ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a1a6a4-0f53-7d68-910a-d324cf9d07ba" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a1a69c-6978-71a8-bb8b-2f25b4dccf0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GeneralAndAdministrativeExpenseLineItems_01a0817f-1eb9-7906-b246-2f4e492bf67a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a1a69c-6978-71a8-bb8b-2f25b4dccf0e" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/AccountsPayableandAccruedLiabilitiesDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#AccountsPayableandAccruedLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/AccountsPayableandAccruedLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:href="tmc-20260930.xsd#tmc_PayablesAndAccrualsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PayablesAndAccrualsTable_01a0817f-1eb9-7e41-869b-27d9528a957f" xlink:href="tmc-20260930.xsd#tmc_PayablesAndAccrualsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:to="loc_tmc_PayablesAndAccrualsTable_01a0817f-1eb9-7e41-869b-27d9528a957f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_PayablesAndAccrualsTable_01a0817f-1eb9-7e41-869b-27d9528a957f" xlink:to="loc_us-gaap_CreditFacilityAxis_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650" xlink:to="loc_us-gaap_CreditFacilityDomain_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a0817f-1eb9-7e08-a940-0e0bb817cc64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a0817f-1eb9-78dc-9bb0-ef53c4dbd650" xlink:to="loc_us-gaap_CreditFacilityDomain_01a0817f-1eb9-7e08-a940-0e0bb817cc64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TwoThousandTwentyFourCreditFacilityMember_01a0817f-1eb9-7c1b-aaf2-5c758727edd7" xlink:href="tmc-20260930.xsd#tmc_TwoThousandTwentyFourCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a0817f-1eb9-7e08-a940-0e0bb817cc64" xlink:to="loc_tmc_TwoThousandTwentyFourCreditFacilityMember_01a0817f-1eb9-7c1b-aaf2-5c758727edd7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7824-940a-44488faedb42" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_PayablesAndAccrualsTable_01a0817f-1eb9-7e41-869b-27d9528a957f" xlink:to="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7824-940a-44488faedb42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7824-940a-44488faedb42_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7824-940a-44488faedb42" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-7824-940a-44488faedb42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-78f1-a489-66ab25936ba5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a0817f-1eb9-7824-940a-44488faedb42" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-78f1-a489-66ab25936ba5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AllseasMember_01a0817f-1eb9-7d24-8f6d-3976614a2548" xlink:href="tmc-20260930.xsd#tmc_AllseasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a0817f-1eb9-78f1-a489-66ab25936ba5" xlink:to="loc_tmc_AllseasMember_01a0817f-1eb9-7d24-8f6d-3976614a2548" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1f0-134c-773b-a8ec-53a7916127d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_tmc_PayablesAndAccrualsTable_01a0817f-1eb9-7e41-869b-27d9528a957f" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1f0-134c-773b-a8ec-53a7916127d9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1b1f0-134c-773b-a8ec-53a7916127d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1f0-134c-773b-a8ec-53a7916127d9" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1b1f0-134c-773b-a8ec-53a7916127d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a1b1f0-134c-7314-bcbf-1b220a6651e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a1b1f0-134c-773b-a8ec-53a7916127d9" xlink:to="loc_us-gaap_RelatedPartyDomain_01a1b1f0-134c-7314-bcbf-1b220a6651e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a1b1f0-3a99-7982-b29e-a4c295d7d98a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a1b1f0-134c-7314-bcbf-1b220a6651e2" xlink:to="loc_us-gaap_RelatedPartyMember_01a1b1f0-3a99-7982-b29e-a4c295d7d98a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_01a0817f-1eb9-732f-8f1f-bcbbb79f93d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:to="loc_us-gaap_AccountsPayableCurrent_01a0817f-1eb9-732f-8f1f-bcbbb79f93d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_01a0817f-1eb9-7f33-9ce1-1fd5a6ebf894" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_01a0817f-1eb9-7f33-9ce1-1fd5a6ebf894" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a0817f-1eb9-7e8f-9b7c-bc1f3ba76eef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a0817f-1eb9-7e8f-9b7c-bc1f3ba76eef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a0817f-1eb9-76d4-ab12-4bddac889ac4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_PayablesAndAccrualsLineItems_01a0817f-1eb9-7d9f-82e3-0ecac33c1615" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a0817f-1eb9-76d4-ab12-4bddac889ac4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/WarrantsPublicWarrantsandPrivateWarrantsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#WarrantsPublicWarrantsandPrivateWarrantsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/WarrantsPublicWarrantsandPrivateWarrantsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7909-8e2e-55fe32e5d3cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7758-982b-9e73b0fc466f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7909-8e2e-55fe32e5d3cc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7758-982b-9e73b0fc466f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7758-982b-9e73b0fc466f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-74fa-ba2b-ae67ab0caa05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-73f7-b5f3-dbbb3de8578b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-74fa-ba2b-ae67ab0caa05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PublicWarrantsMember_01a0817f-1eb9-7bb4-bfba-22b5f95247f0" xlink:href="tmc-20260930.xsd#tmc_PublicWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-74fa-ba2b-ae67ab0caa05" xlink:to="loc_tmc_PublicWarrantsMember_01a0817f-1eb9-7bb4-bfba-22b5f95247f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PrivatePlacementWarrantsMember_01a0817f-1eb9-708f-9149-4237a19a8db3" xlink:href="tmc-20260930.xsd#tmc_PrivatePlacementWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-74fa-ba2b-ae67ab0caa05" xlink:to="loc_tmc_PrivatePlacementWarrantsMember_01a0817f-1eb9-708f-9149-4237a19a8db3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a0817f-1eb9-70a2-9cae-101bad186fe3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7909-8e2e-55fe32e5d3cc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a0817f-1eb9-70a2-9cae-101bad186fe3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a0817f-1eb9-7116-abb8-f0bd144cb52d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7909-8e2e-55fe32e5d3cc" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a0817f-1eb9-7116-abb8-f0bd144cb52d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_01a0817f-1eb9-70c2-8815-6b1522531b55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7909-8e2e-55fe32e5d3cc" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_01a0817f-1eb9-70c2-8815-6b1522531b55" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/WarrantsScheduleofChangesinFairValueofWarrantLiabilityDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#WarrantsScheduleofChangesinFairValueofWarrantLiabilityDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/WarrantsScheduleofChangesinFairValueofWarrantLiabilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7a9f-99dd-61aa396cb34f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-78dc-8682-33924cf82def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7a9f-99dd-61aa396cb34f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-78dc-8682-33924cf82def" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1b1f3-c861-7adc-9d02-256cb4e606ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-78dc-8682-33924cf82def" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1b1f3-c861-7adc-9d02-256cb4e606ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1b1f3-c861-7adc-9d02-256cb4e606ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1b1f3-c861-7adc-9d02-256cb4e606ff" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1b1f3-c861-7adc-9d02-256cb4e606ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1b1f3-c861-7233-b105-aedb07f1fe0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1b1f3-c861-7adc-9d02-256cb4e606ff" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1b1f3-c861-7233-b105-aedb07f1fe0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PrivatePlacementWarrantsMember_01a1b1f3-c861-7461-b80c-16c6bfb94c1b" xlink:href="tmc-20260930.xsd#tmc_PrivatePlacementWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1b1f3-c861-7233-b105-aedb07f1fe0f" xlink:to="loc_tmc_PrivatePlacementWarrantsMember_01a1b1f3-c861-7461-b80c-16c6bfb94c1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01a1a618-b72e-7af7-a75e-2c9c70c161fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7a9f-99dd-61aa396cb34f" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01a1a618-b72e-7af7-a75e-2c9c70c161fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityValue_01a0817f-1eb9-704c-91ab-ef9d0aad06a6" xlink:href="tmc-20260930.xsd#tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01a1a618-b72e-7af7-a75e-2c9c70c161fa" xlink:to="loc_tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityValue_01a0817f-1eb9-704c-91ab-ef9d0aad06a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityGainLoss_01a0817f-1eb9-75d7-9eff-cff50d224a39" xlink:href="tmc-20260930.xsd#tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_01a1a618-b72e-7af7-a75e-2c9c70c161fa" xlink:to="loc_tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityGainLoss_01a0817f-1eb9-75d7-9eff-cff50d224a39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityValue_01a0817f-1eb9-78cb-a88e-f2678ff861f7" xlink:href="tmc-20260930.xsd#tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/WarrantsClassAClassBClassCKoreaZincNaoeroandTongaWarrantsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#WarrantsClassAClassBClassCKoreaZincNaoeroandTongaWarrantsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/WarrantsClassAClassBClassCKoreaZincNaoeroandTongaWarrantsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7d6c-9375-0b09466c7362" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7d6c-9375-0b09466c7362" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7b53-ad0a-37770058d16b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_01a0817f-1eb9-7d6c-9375-0b09466c7362" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7b53-ad0a-37770058d16b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7b53-ad0a-37770058d16b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7b53-ad0a-37770058d16b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7b53-ad0a-37770058d16b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a0817f-1eb9-7b53-ad0a-37770058d16b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-70df-ab87-d4fda5aee886" xlink:href="tmc-20260930.xsd#tmc_ClassAWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_ClassAWarrantsMember_01a0817f-1eb9-70df-ab87-d4fda5aee886" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-756c-b18d-47b41137ac15" xlink:href="tmc-20260930.xsd#tmc_ClassBWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_ClassBWarrantsMember_01a0817f-1eb9-756c-b18d-47b41137ac15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassCWarrantsMember_01a0817f-1eb9-7689-8b55-5d6ceeba66e3" xlink:href="tmc-20260930.xsd#tmc_ClassCWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_ClassCWarrantsMember_01a0817f-1eb9-7689-8b55-5d6ceeba66e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_KoreaZincWarrantsMember_01a0817f-1eb9-78fa-9181-8a1dc23bb1a5" xlink:href="tmc-20260930.xsd#tmc_KoreaZincWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_KoreaZincWarrantsMember_01a0817f-1eb9-78fa-9181-8a1dc23bb1a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NaoeroWarrantsMember_01a0817f-1eb9-7a9e-a52b-8954ed0981aa" xlink:href="tmc-20260930.xsd#tmc_NaoeroWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_NaoeroWarrantsMember_01a0817f-1eb9-7a9e-a52b-8954ed0981aa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TongaWarrantsMember_01a0817f-1eb9-7926-b44a-a7ffed432194" xlink:href="tmc-20260930.xsd#tmc_TongaWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a0817f-1eb9-7dc5-98e6-ce57d966fa01" xlink:to="loc_tmc_TongaWarrantsMember_01a0817f-1eb9-7926-b44a-a7ffed432194" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a0817f-1eb9-7bb6-b995-63e827e529b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a0817f-1eb9-7bb6-b995-63e827e529b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_01a15e9b-be9b-7b71-b4bf-fcf6987fb647" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_01a15e9b-be9b-7b71-b4bf-fcf6987fb647" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a15e9b-be9b-71b6-823f-38fe51f520ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a15e9b-be9b-71b6-823f-38fe51f520ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ClassOfWarrantOrRightExercised_01a15e9c-17d3-7c6d-9785-138f3b690aef" xlink:href="tmc-20260930.xsd#tmc_ClassOfWarrantOrRightExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_tmc_ClassOfWarrantOrRightExercised_01a15e9c-17d3-7c6d-9785-138f3b690aef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_01a15e9c-17d3-7fac-bd6a-1dcb8456a29c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_01a0817f-1eb9-7f38-8d74-ab6b6fa039fe" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_01a15e9c-17d3-7fac-bd6a-1dcb8456a29c" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-709c-b96b-84c1d14e4e54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-709c-b96b-84c1d14e4e54" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a15eba-ae64-7af0-a004-e64287f662a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-709c-b96b-84c1d14e4e54" xlink:to="loc_us-gaap_PlanNameAxis_01a15eba-ae64-7af0-a004-e64287f662a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a15eba-ae64-7af0-a004-e64287f662a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_01a15eba-ae64-7af0-a004-e64287f662a9" xlink:to="loc_us-gaap_PlanNameDomain_01a15eba-ae64-7af0-a004-e64287f662a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a15eba-ae64-7cd9-9f0c-c31c586e0d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_01a15eba-ae64-7af0-a004-e64287f662a9" xlink:to="loc_us-gaap_PlanNameDomain_01a15eba-ae64-7cd9-9f0c-c31c586e0d4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_IncentiveEquityPlan2021Member_01a15eba-ae64-7d98-87a9-0d13ba2831bd" xlink:href="tmc-20260930.xsd#tmc_IncentiveEquityPlan2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a15eba-ae64-7cd9-9f0c-c31c586e0d4c" xlink:to="loc_tmc_IncentiveEquityPlan2021Member_01a15eba-ae64-7d98-87a9-0d13ba2831bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_01a15eba-ae64-7928-8944-72ee2eb4ac97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_01a15eba-ae64-7928-8944-72ee2eb4ac97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorizedSubjectToApproval_01a15eba-ae64-72db-87a4-d91163c5f051" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorizedSubjectToApproval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorizedSubjectToApproval_01a15eba-ae64-72db-87a4-d91163c5f051" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_01a15eba-ae64-79b7-b0ea-3ecd2a9edbd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_01a15eba-ae64-79b7-b0ea-3ecd2a9edbd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_CommonShareIssuedAndOutstandingPercentage_01a1a7cc-b24a-7b7a-810c-7bf2286590dc" xlink:href="tmc-20260930.xsd#tmc_CommonShareIssuedAndOutstandingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-738e-b206-4e9c1afa9205" xlink:to="loc_tmc_CommonShareIssuedAndOutstandingPercentage_01a1a7cc-b24a-7b7a-810c-7bf2286590dc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationScheduleofMovementofStockOptionsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationScheduleofMovementofStockOptionsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationScheduleofMovementofStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7c03-a1bc-169ee8baa5cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-70e0-b341-4bc333467166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7c03-a1bc-169ee8baa5cb" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-70e0-b341-4bc333467166" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a0817f-1eb9-7757-bbd3-dc354f65355c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-70e0-b341-4bc333467166" xlink:to="loc_us-gaap_PlanNameAxis_01a0817f-1eb9-7757-bbd3-dc354f65355c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7757-bbd3-dc354f65355c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_01a0817f-1eb9-7757-bbd3-dc354f65355c" xlink:to="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7757-bbd3-dc354f65355c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7cfc-8b30-d47fc71a9ac6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_01a0817f-1eb9-7757-bbd3-dc354f65355c" xlink:to="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7cfc-8b30-d47fc71a9ac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShortTermIncentivePlanMember_01a0817f-1eb9-76b7-8607-573bd7726ab3" xlink:href="tmc-20260930.xsd#tmc_ShortTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7cfc-8b30-d47fc71a9ac6" xlink:to="loc_tmc_ShortTermIncentivePlanMember_01a0817f-1eb9-76b7-8607-573bd7726ab3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_LongtermIncentivePlanMember_01a0817f-1eb9-705f-a8a8-8a9e71a31d99" xlink:href="tmc-20260930.xsd#tmc_LongtermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7cfc-8b30-d47fc71a9ac6" xlink:to="loc_tmc_LongtermIncentivePlanMember_01a0817f-1eb9-705f-a8a8-8a9e71a31d99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TwentyTwentyOneIncentivePlanMember_01a0817f-1eb9-774d-a1ee-d5520ecb0332" xlink:href="tmc-20260930.xsd#tmc_TwentyTwentyOneIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a0817f-1eb9-7cfc-8b30-d47fc71a9ac6" xlink:to="loc_tmc_TwentyTwentyOneIncentivePlanMember_01a0817f-1eb9-774d-a1ee-d5520ecb0332" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7c03-a1bc-169ee8baa5cb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a0817f-1eb9-7322-b589-c6d3f0ac37dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a0817f-1eb9-7322-b589-c6d3f0ac37dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a0817f-1eb9-7a2e-9f80-370e4b486578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a0817f-1eb9-7a2e-9f80-370e4b486578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_01a0817f-1eb9-7838-a116-16aff5213ec6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_01a0817f-1eb9-7838-a116-16aff5213ec6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_01a1b1d0-ea10-79f6-b90e-7d3ff421dda1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a1a55b-a002-7e52-b62d-5170b7d99647" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_01a1b1d0-ea10-79f6-b90e-7d3ff421dda1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a0817f-1eb9-76ce-83f4-62bdede8083d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationStockOptionsNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationStockOptionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationStockOptionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:to="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7491-b302-c6d7d40f9281_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7491-b302-c6d7d40f9281_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a1a7cb-fd89-7792-8e3a-0864c96a3e72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a1a7cb-fd89-7792-8e3a-0864c96a3e72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a1a7cb-fd89-727f-9978-77d5f3925953" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a1a7cb-fd89-727f-9978-77d5f3925953" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cb-fd89-70cb-b259-8daa2e339590" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cb-fd89-70cb-b259-8daa2e339590" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationStockOptionsNarrativeDetails_1" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationStockOptionsNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationStockOptionsNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cb-fd89-7633-8664-c4541fbd5703" xlink:to="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7491-b302-c6d7d40f9281_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7491-b302-c6d7d40f9281_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cb-fd89-7491-b302-c6d7d40f9281" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a1a7cb-fd89-7792-8e3a-0864c96a3e72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cb-fd89-7ba8-b583-7206ef68ea01" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a1a7cb-fd89-7792-8e3a-0864c96a3e72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cb-fd89-70cb-b259-8daa2e339590" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cb-fd89-7ac4-a1a4-3aa2a3b2ce49" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cb-fd89-70cb-b259-8daa2e339590" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationScheduleofRSUActivityDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationScheduleofRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationScheduleofRSUActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7fee-bc7a-53d730553704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7654-8350-ecc1db54526f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7fee-bc7a-53d730553704" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7654-8350-ecc1db54526f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7971-93cb-2d2c95ffd27c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7654-8350-ecc1db54526f" xlink:to="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7971-93cb-2d2c95ffd27c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7971-93cb-2d2c95ffd27c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7971-93cb-2d2c95ffd27c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7971-93cb-2d2c95ffd27c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-795a-ae7e-69de03f95e60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7971-93cb-2d2c95ffd27c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-795a-ae7e-69de03f95e60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-73f4-b2ad-c92731cb0c40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-795a-ae7e-69de03f95e60" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-73f4-b2ad-c92731cb0c40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7fee-bc7a-53d730553704" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a0817f-1eb9-7b03-9ff5-405382b874e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a0817f-1eb9-7b03-9ff5-405382b874e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7068-a797-2d69b77d7f18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7068-a797-2d69b77d7f18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_01a0817f-1eb9-716c-8812-1ccfee4e3239" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_01a0817f-1eb9-716c-8812-1ccfee4e3239" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod_01a0817f-1eb9-7e42-a8b0-c9dd6f242f82" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_01a0817f-1eb9-7e4b-a123-df756ace4d48" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriod_01a0817f-1eb9-7e42-a8b0-c9dd6f242f82" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a0817f-1eb9-76b7-886e-259982a2dd76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationScheduleofRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationScheduleofRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationScheduleofRestrictedStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_01a0817f-1eb9-7be4-9b27-6e8caa587cbd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:to="loc_us-gaap_VestingDomain_01a0817f-1eb9-7be4-9b27-6e8caa587cbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:to="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_01a0817f-1eb9-763a-909e-deee8af3c9f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_01a0817f-1eb9-763a-909e-deee8af3c9f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_01a0817f-1eb9-7759-93e2-db7259374a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_01a0817f-1eb9-7759-93e2-db7259374a80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember_01a1ad3f-0db3-756b-bd2d-f32aa181437b" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember_01a1ad3f-0db3-756b-bd2d-f32aa181437b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember_01a1ad3f-427d-7cd7-ac54-daf7f60fabb9" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember_01a1ad3f-427d-7cd7-ac54-daf7f60fabb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember_01a1ad3f-71dc-71e0-9cea-66c3ce004d4f" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember_01a1ad3f-71dc-71e0-9cea-66c3ce004d4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember_01a1ad40-62aa-704a-a522-a135b9c386c6" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember_01a1ad40-62aa-704a-a522-a135b9c386c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember_01a1ad40-830d-72c8-8c11-9458cd33d4eb" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember_01a1ad40-830d-72c8-8c11-9458cd33d4eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember_01a1ad40-a646-791f-9aaa-501912cc11be" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember_01a1ad40-a646-791f-9aaa-501912cc11be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember_01a1ad40-c4b0-7f5d-8db0-d6a382ca0ae6" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember_01a1ad40-c4b0-7f5d-8db0-d6a382ca0ae6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFiveMember_01a0817f-1eb9-7020-8c03-8c339f257414" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFiveMember_01a0817f-1eb9-7020-8c03-8c339f257414" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheSixMember_01a1a22b-4260-7baf-886f-7f6cf6d88763" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheSixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheSixMember_01a1a22b-4260-7baf-886f-7f6cf6d88763" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember_01a0817f-1eb9-73be-a232-d5405a85c113" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember_01a0817f-1eb9-73be-a232-d5405a85c113" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember_01a1a22b-4260-7aca-9e67-1e17dd960939" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember_01a1a22b-4260-7aca-9e67-1e17dd960939" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7d33-9f5f-1bfc295afb70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7d33-9f5f-1bfc295afb70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-7a80-8213-89b6ca0a7a95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:to="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-7a80-8213-89b6ca0a7a95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:to="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ConsultantsMember_01a0817f-1eb9-7b9c-8e5c-3dc7b84cf5f6" xlink:href="tmc-20260930.xsd#tmc_ConsultantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_tmc_ConsultantsMember_01a0817f-1eb9-7b9c-8e5c-3dc7b84cf5f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a0817f-1eb9-7fce-8c53-e47cb82d28e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a0817f-1eb9-7fce-8c53-e47cb82d28e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a0817f-1eb9-7078-b73b-289b8fde86b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a0817f-1eb9-7078-b73b-289b8fde86b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a0817f-1eb9-7517-9934-3cd3b6175008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a0817f-1eb9-7517-9934-3cd3b6175008" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-7cbd-a302-6962874717f7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-7cbd-a302-6962874717f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NonEmployeeDirectorsMember_01a0817f-1eb9-70f5-9629-a382d25e641e" xlink:href="tmc-20260930.xsd#tmc_NonEmployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:to="loc_tmc_NonEmployeeDirectorsMember_01a0817f-1eb9-70f5-9629-a382d25e641e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_01a1a271-076d-74a3-a6b8-43daa3691030" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:to="loc_srt_DirectorMember_01a1a271-076d-74a3-a6b8-43daa3691030" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:href="tmc-20260930.xsd#tmc_AwardGrantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantDomain_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0_default" xlink:href="tmc-20260930.xsd#tmc_AwardGrantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:to="loc_tmc_AwardGrantDomain_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:href="tmc-20260930.xsd#tmc_AwardGrantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:to="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_InitialGrantMember_01a1a278-8de8-7ee4-b19c-9106e9cccecc" xlink:href="tmc-20260930.xsd#tmc_InitialGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:to="loc_tmc_InitialGrantMember_01a1a278-8de8-7ee4-b19c-9106e9cccecc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SpecialRetentionGrantMember_01a1a27a-2c51-7459-bdd2-aa4adb92f2a4" xlink:href="tmc-20260930.xsd#tmc_SpecialRetentionGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:to="loc_tmc_SpecialRetentionGrantMember_01a1a27a-2c51-7459-bdd2-aa4adb92f2a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7508-9f31-68b8eefb6ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7508-9f31-68b8eefb6ef0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_01a0817f-1eb9-7e3b-af1b-4f6a2526a02a" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_01a0817f-1eb9-7e3b-af1b-4f6a2526a02a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_01a1ad3b-9aa4-76af-b0a9-c792266a9677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_01a1ad3b-9aa4-76af-b0a9-c792266a9677" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a1ad3b-6540-727a-80d3-b00514bb602c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a1ad3b-6540-727a-80d3-b00514bb602c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded_01a1b1fb-f0bd-7e5d-b72f-ff9182a6df96" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded_01a1b1fb-f0bd-7e5d-b72f-ff9182a6df96" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationScheduleofRestrictedStockUnitsDetails_1" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationScheduleofRestrictedStockUnitsDetails_1"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationScheduleofRestrictedStockUnitsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_01a0817f-1eb9-7be4-9b27-6e8caa587cbd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:to="loc_us-gaap_VestingDomain_01a0817f-1eb9-7be4-9b27-6e8caa587cbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_01a0817f-1eb9-7be4-9b27-6e8caa587cbd" xlink:to="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_01a0817f-1eb9-763a-909e-deee8af3c9f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_01a0817f-1eb9-763a-909e-deee8af3c9f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_01a0817f-1eb9-7759-93e2-db7259374a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_01a0817f-1eb9-7759-93e2-db7259374a80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember_01a1ad3f-0db3-756b-bd2d-f32aa181437b" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearOneMember_01a1ad3f-0db3-756b-bd2d-f32aa181437b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember_01a1ad3f-427d-7cd7-ac54-daf7f60fabb9" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearTwoMember_01a1ad3f-427d-7cd7-ac54-daf7f60fabb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember_01a1ad3f-71dc-71e0-9cea-66c3ce004d4f" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_01a0817f-1eb9-7ea9-890f-2157078a1df4" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheThreeYearThreeMember_01a1ad3f-71dc-71e0-9cea-66c3ce004d4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember_01a1ad40-62aa-704a-a522-a135b9c386c6" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearOneMember_01a1ad40-62aa-704a-a522-a135b9c386c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember_01a1ad40-830d-72c8-8c11-9458cd33d4eb" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearTwoMember_01a1ad40-830d-72c8-8c11-9458cd33d4eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember_01a1ad40-a646-791f-9aaa-501912cc11be" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearThreeMember_01a1ad40-a646-791f-9aaa-501912cc11be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember_01a1ad40-c4b0-7f5d-8db0-d6a382ca0ae6" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_ShareBasedPaymentArrangementTrancheFourMember_01a0817f-1eb9-7022-973b-c227e34359cd" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFourYearFourMember_01a1ad40-c4b0-7f5d-8db0-d6a382ca0ae6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheFiveMember_01a0817f-1eb9-7020-8c03-8c339f257414" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheFiveMember_01a0817f-1eb9-7020-8c03-8c339f257414" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementTrancheSixMember_01a1a22b-4260-7baf-886f-7f6cf6d88763" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementTrancheSixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementTrancheSixMember_01a1a22b-4260-7baf-886f-7f6cf6d88763" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember_01a0817f-1eb9-73be-a232-d5405a85c113" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnPerformanceConditionsMember_01a0817f-1eb9-73be-a232-d5405a85c113" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember_01a1a22b-4260-7aca-9e67-1e17dd960939" xlink:href="tmc-20260930.xsd#tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_01a0817f-1eb9-7ab3-8164-e73c6617695b" xlink:to="loc_tmc_ShareBasedPaymentArrangementVestingBasedOnMarketConditionsMember_01a1a22b-4260-7aca-9e67-1e17dd960939" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a0817f-1eb9-7eea-8880-8cfbf06dc2c4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7d33-9f5f-1bfc295afb70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a0817f-1eb9-7dd2-b4b7-73412a8e8ffb" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a0817f-1eb9-7d33-9f5f-1bfc295afb70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-7a80-8213-89b6ca0a7a95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:to="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-7a80-8213-89b6ca0a7a95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_01a0817f-1eb9-7a80-8213-89b6ca0a7a95" xlink:to="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ConsultantsMember_01a0817f-1eb9-7b9c-8e5c-3dc7b84cf5f6" xlink:href="tmc-20260930.xsd#tmc_ConsultantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_tmc_ConsultantsMember_01a0817f-1eb9-7b9c-8e5c-3dc7b84cf5f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a0817f-1eb9-7fce-8c53-e47cb82d28e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a0817f-1eb9-7fce-8c53-e47cb82d28e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a0817f-1eb9-7078-b73b-289b8fde86b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a0817f-1eb9-776c-904c-d656e38077c9" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a0817f-1eb9-7078-b73b-289b8fde86b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-7cbd-a302-6962874717f7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-7cbd-a302-6962874717f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_01a0817f-1eb9-7cbd-a302-6962874717f7" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NonEmployeeDirectorsMember_01a0817f-1eb9-70f5-9629-a382d25e641e" xlink:href="tmc-20260930.xsd#tmc_NonEmployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:to="loc_tmc_NonEmployeeDirectorsMember_01a0817f-1eb9-70f5-9629-a382d25e641e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_01a1a271-076d-74a3-a6b8-43daa3691030" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_01a0817f-1eb9-77c5-af37-275ecb1c8111" xlink:to="loc_srt_DirectorMember_01a1a271-076d-74a3-a6b8-43daa3691030" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:href="tmc-20260930.xsd#tmc_AwardGrantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-7425-b041-e8e781ac5883" xlink:to="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantDomain_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0_default" xlink:href="tmc-20260930.xsd#tmc_AwardGrantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:to="loc_tmc_AwardGrantDomain_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:href="tmc-20260930.xsd#tmc_AwardGrantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_tmc_AwardGrantAxis_01a1a277-f53f-7a7d-a3f4-7134cce0ddd0" xlink:to="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_InitialGrantMember_01a1a278-8de8-7ee4-b19c-9106e9cccecc" xlink:href="tmc-20260930.xsd#tmc_InitialGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:to="loc_tmc_InitialGrantMember_01a1a278-8de8-7ee4-b19c-9106e9cccecc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SpecialRetentionGrantMember_01a1a27a-2c51-7459-bdd2-aa4adb92f2a4" xlink:href="tmc-20260930.xsd#tmc_SpecialRetentionGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AwardGrantDomain_01a1a277-f53f-7abb-9d87-88fd7cff4341" xlink:to="loc_tmc_SpecialRetentionGrantMember_01a1a27a-2c51-7459-bdd2-aa4adb92f2a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7508-9f31-68b8eefb6ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a0817f-1eb9-7508-9f31-68b8eefb6ef0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_01a0817f-1eb9-7e3b-af1b-4f6a2526a02a" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue_01a0817f-1eb9-7e3b-af1b-4f6a2526a02a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_01a1ad3b-9aa4-76af-b0a9-c792266a9677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_01a1ad3b-9aa4-76af-b0a9-c792266a9677" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a1ad3b-6540-727a-80d3-b00514bb602c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_01a1ad3b-6540-727a-80d3-b00514bb602c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded_01a1b1fb-f0bd-7e5d-b72f-ff9182a6df96" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7190-aa4b-6d947273f95a" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfDirectorsAwarded_01a1b1fb-f0bd-7e5d-b72f-ff9182a6df96" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationRestrictedShareUnitsNarrativeDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationRestrictedShareUnitsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationRestrictedShareUnitsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:to="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-77ac-97fa-11648fb157a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-77ac-97fa-11648fb157a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a1a7cc-1628-7472-bd14-9d5815525171" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a1a7cc-1628-7472-bd14-9d5815525171" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a1a7cc-1628-738c-99eb-63a78132c184" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a1a7cc-1628-738c-99eb-63a78132c184" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested_01a1d07d-43f7-798a-bf44-aa1f0bf451e9" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested_01a1d07d-43f7-798a-bf44-aa1f0bf451e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cc-1628-75cf-8bef-81a2d39373d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cc-1628-75cf-8bef-81a2d39373d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a1a7cc-1628-7ad1-8a8c-0de9d9def9d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a1a7cc-1628-7ad1-8a8c-0de9d9def9d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a1a7cc-1628-7cc7-af5c-d2e54cf880e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a1a7cc-1628-7cc7-af5c-d2e54cf880e8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationRestrictedShareUnitsNarrativeDetails_1" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationRestrictedShareUnitsNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationRestrictedShareUnitsNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a1a7cc-1628-771b-ac33-69766e0f96d4" xlink:to="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-77ac-97fa-11648fb157a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-77ac-97fa-11648fb157a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a1a7cc-1628-77ac-97fa-11648fb157a0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a1a7cc-1628-7472-bd14-9d5815525171" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a1a7cc-1628-76f7-bffb-cec9b7667dd6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a1a7cc-1628-7472-bd14-9d5815525171" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested_01a1d07d-43f7-798a-bf44-aa1f0bf451e9" xlink:href="tmc-20260930.xsd#tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNumberOfCommonSharesIssuedForEachRestrictedStockUnitVested_01a1d07d-43f7-798a-bf44-aa1f0bf451e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cc-1628-75cf-8bef-81a2d39373d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a1a7cc-1628-75cf-8bef-81a2d39373d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a1a7cc-1628-7ad1-8a8c-0de9d9def9d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a1a7cc-1628-7ad1-8a8c-0de9d9def9d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a1a7cc-1628-7cc7-af5c-d2e54cf880e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a1a7cc-1628-7c69-bbaf-d2ad061ae7d0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a1a7cc-1628-7cc7-af5c-d2e54cf880e8" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ShareBasedCompensationEmployeeStockPurchasePlanDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ShareBasedCompensationEmployeeStockPurchasePlanDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ShareBasedCompensationEmployeeStockPurchasePlanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-79b2-b094-b3d9fcd0e83a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-79b2-b094-b3d9fcd0e83a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a15ea3-9b34-7a61-806f-6db6047e926d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-79b2-b094-b3d9fcd0e83a" xlink:to="loc_us-gaap_AwardTypeAxis_01a15ea3-9b34-7a61-806f-6db6047e926d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15ea3-9b34-7a61-806f-6db6047e926d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a15ea3-9b34-7a61-806f-6db6047e926d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15ea3-9b34-7a61-806f-6db6047e926d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15ea3-9b34-7aac-a2d0-6dbc9a86aa21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a15ea3-9b34-7a61-806f-6db6047e926d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15ea3-9b34-7aac-a2d0-6dbc9a86aa21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EmployeeSharePurchasePlanMember_01a15ea3-9b34-73b0-9ee0-987b52ea30ee" xlink:href="tmc-20260930.xsd#tmc_EmployeeSharePurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a15ea3-9b34-7aac-a2d0-6dbc9a86aa21" xlink:to="loc_tmc_EmployeeSharePurchasePlanMember_01a15ea3-9b34-73b0-9ee0-987b52ea30ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a15ea3-9b34-7548-9573-48137c88e7cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a0817f-1eb9-79b2-b094-b3d9fcd0e83a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a15ea3-9b34-7548-9573-48137c88e7cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a15ea3-9b34-7548-9573-48137c88e7cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a15ea3-9b34-7548-9573-48137c88e7cf" xlink:to="loc_us-gaap_ClassOfStockDomain_01a15ea3-9b34-7548-9573-48137c88e7cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a15ea3-9b34-7ba8-ad6a-889b5f38dbdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a15ea3-9b34-7548-9573-48137c88e7cf" xlink:to="loc_us-gaap_ClassOfStockDomain_01a15ea3-9b34-7ba8-ad6a-889b5f38dbdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a15ea3-9b34-727e-a336-98556b6170a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a15ea3-9b34-7ba8-ad6a-889b5f38dbdf" xlink:to="loc_us-gaap_CommonStockMember_01a15ea3-9b34-727e-a336-98556b6170a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_01a1a6c3-1136-7c00-b205-e28007ab93eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_01a1a6c3-1136-7c00-b205-e28007ab93eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_01a15ea3-9b34-76dd-8b99-22330880e881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_01a15ea3-9b34-76dd-8b99-22330880e881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PercentageOfCommonStockSharesOutstanding_01a15ea3-9b34-7cf3-a3b5-f3b0b2f61f7e" xlink:href="tmc-20260930.xsd#tmc_PercentageOfCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_tmc_PercentageOfCommonStockSharesOutstanding_01a15ea3-9b34-7cf3-a3b5-f3b0b2f61f7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a15ea5-d041-79e8-88fd-ff72f498ebd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a15ea5-d041-79e8-88fd-ff72f498ebd4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a15ea6-6a66-7632-873f-622fcfbcfc2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a0817f-1eb9-7dd5-a198-e8be3c333529" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a15ea6-6a66-7632-873f-622fcfbcfc2b" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/LossperShareDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#LossperShareDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/LossperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a0817f-1eb9-7f8a-94d6-3addb6b43ea0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a0817f-1eb9-74b7-9be1-2c2b3de221ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a0817f-1eb9-7f8a-94d6-3addb6b43ea0" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a0817f-1eb9-74b7-9be1-2c2b3de221ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a0817f-1eb9-788b-aa02-96acfc009f5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a0817f-1eb9-74b7-9be1-2c2b3de221ac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a0817f-1eb9-788b-aa02-96acfc009f5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-788b-aa02-96acfc009f5c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a0817f-1eb9-788b-aa02-96acfc009f5c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-788b-aa02-96acfc009f5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a0817f-1eb9-788b-aa02-96acfc009f5c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a0817f-1eb9-7205-9462-fd95a6a280d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a0817f-1eb9-7205-9462-fd95a6a280d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_01a0817f-1eb9-749c-aa63-4fb8d3c62e20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:to="loc_us-gaap_RestrictedStockMember_01a0817f-1eb9-749c-aa63-4fb8d3c62e20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_EmployeeSharePurchasePlanMember_01a0817f-1eb9-7d3e-b80c-91cd9b650195" xlink:href="tmc-20260930.xsd#tmc_EmployeeSharePurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:to="loc_tmc_EmployeeSharePurchasePlanMember_01a0817f-1eb9-7d3e-b80c-91cd9b650195" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_01a0817f-1eb9-7508-bdd6-132ce0e133e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:to="loc_us-gaap_WarrantMember_01a0817f-1eb9-7508-bdd6-132ce0e133e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_SpecialSharesAndOptionsToPurchaseSpecialSharesMember_01a0817f-1eb9-7ab9-87ea-84fd95cfaeb4" xlink:href="tmc-20260930.xsd#tmc_SpecialSharesAndOptionsToPurchaseSpecialSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a0817f-1eb9-7786-a999-8e77afd64177" xlink:to="loc_tmc_SpecialSharesAndOptionsToPurchaseSpecialSharesMember_01a0817f-1eb9-7ab9-87ea-84fd95cfaeb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a0817f-1eb9-780e-bb95-193e9e23ae08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a0817f-1eb9-7f8a-94d6-3addb6b43ea0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a0817f-1eb9-780e-bb95-193e9e23ae08" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/FinancialInstrumentsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#FinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/FinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a0817f-1eb9-7574-a0c4-a2023e76fb61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a0817f-1eb9-75d0-92a2-f34b8aff1e50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a0817f-1eb9-7574-a0c4-a2023e76fb61" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a0817f-1eb9-75d0-92a2-f34b8aff1e50" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a0817f-1eb9-728c-964f-f6a3817aa5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_01a0817f-1eb9-75d0-92a2-f34b8aff1e50" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a0817f-1eb9-728c-964f-f6a3817aa5a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a0817f-1eb9-728c-964f-f6a3817aa5a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a0817f-1eb9-728c-964f-f6a3817aa5a3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a0817f-1eb9-728c-964f-f6a3817aa5a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a0817f-1eb9-79cf-a550-cf939f3bce8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a0817f-1eb9-728c-964f-f6a3817aa5a3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a0817f-1eb9-79cf-a550-cf939f3bce8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a0817f-1eb9-7598-b316-8e9d3c09e160" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a0817f-1eb9-79cf-a550-cf939f3bce8a" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a0817f-1eb9-7598-b316-8e9d3c09e160" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FinancialAssetsAbstract_01a0817f-1eb9-7f3e-87ce-cc397bd75b0f" xlink:href="tmc-20260930.xsd#tmc_FinancialAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a0817f-1eb9-7574-a0c4-a2023e76fb61" xlink:to="loc_tmc_FinancialAssetsAbstract_01a0817f-1eb9-7f3e-87ce-cc397bd75b0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AmortizedCostAbstract_01a0817f-1eb9-7c47-bf80-822e9d7efe7f" xlink:href="tmc-20260930.xsd#tmc_AmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FinancialAssetsAbstract_01a0817f-1eb9-7f3e-87ce-cc397bd75b0f" xlink:to="loc_tmc_AmortizedCostAbstract_01a0817f-1eb9-7c47-bf80-822e9d7efe7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a0817f-1eb9-7010-8597-d9eec645dcf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AmortizedCostAbstract_01a0817f-1eb9-7c47-bf80-822e9d7efe7f" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_01a0817f-1eb9-7010-8597-d9eec645dcf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TaxesAndOtherReceivablesCurrent_01a0817f-1eb9-7721-93dc-c06ba756ba91" xlink:href="tmc-20260930.xsd#tmc_TaxesAndOtherReceivablesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AmortizedCostAbstract_01a0817f-1eb9-7c47-bf80-822e9d7efe7f" xlink:to="loc_tmc_TaxesAndOtherReceivablesCurrent_01a0817f-1eb9-7721-93dc-c06ba756ba91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FinancialAssets_01a0817f-1eb9-79d6-8fcc-ae5221ed4fa5" xlink:href="tmc-20260930.xsd#tmc_FinancialAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AmortizedCostAbstract_01a0817f-1eb9-7c47-bf80-822e9d7efe7f" xlink:to="loc_tmc_FinancialAssets_01a0817f-1eb9-79d6-8fcc-ae5221ed4fa5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FinancialLiabilitiesAbstract_01a0817f-1eb9-746c-a254-bde15454d743" xlink:href="tmc-20260930.xsd#tmc_FinancialLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_01a0817f-1eb9-7574-a0c4-a2023e76fb61" xlink:to="loc_tmc_FinancialLiabilitiesAbstract_01a0817f-1eb9-746c-a254-bde15454d743" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AmortizedCostAbstract0_01a0817f-1eb9-73b7-8eec-42f9cfac941f" xlink:href="tmc-20260930.xsd#tmc_AmortizedCostAbstract0"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FinancialLiabilitiesAbstract_01a0817f-1eb9-746c-a254-bde15454d743" xlink:to="loc_tmc_AmortizedCostAbstract0_01a0817f-1eb9-73b7-8eec-42f9cfac941f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a0817f-1eb9-7156-954e-e9a769fcffd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_AmortizedCostAbstract0_01a0817f-1eb9-73b7-8eec-42f9cfac941f" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a0817f-1eb9-7156-954e-e9a769fcffd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FairValueThroughProfitOrLossAbstract_01a18ceb-049f-7d58-a8fd-03549d491bc3" xlink:href="tmc-20260930.xsd#tmc_FairValueThroughProfitOrLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FinancialLiabilitiesAbstract_01a0817f-1eb9-746c-a254-bde15454d743" xlink:to="loc_tmc_FairValueThroughProfitOrLossAbstract_01a18ceb-049f-7d58-a8fd-03549d491bc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_AccruedRoyaltiesNonCurrent_01a0817f-1eb9-7179-913a-35d15734ae0d" xlink:href="tmc-20260930.xsd#tmc_AccruedRoyaltiesNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FairValueThroughProfitOrLossAbstract_01a18ceb-049f-7d58-a8fd-03549d491bc3" xlink:to="loc_tmc_AccruedRoyaltiesNonCurrent_01a0817f-1eb9-7179-913a-35d15734ae0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_WarrantLiability_01a0817f-1eb9-71f8-aa3b-640cdbae4d70" xlink:href="tmc-20260930.xsd#tmc_WarrantLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FairValueThroughProfitOrLossAbstract_01a18ceb-049f-7d58-a8fd-03549d491bc3" xlink:to="loc_tmc_WarrantLiability_01a0817f-1eb9-71f8-aa3b-640cdbae4d70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FinancialLiabilities_01a0817f-1eb9-75ad-8b9e-152fe1120b85" xlink:href="tmc-20260930.xsd#tmc_FinancialLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_FairValueThroughProfitOrLossAbstract_01a18ceb-049f-7d58-a8fd-03549d491bc3" xlink:to="loc_tmc_FinancialLiabilities_01a0817f-1eb9-75ad-8b9e-152fe1120b85" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fb-b7c2-79d8980e6f99_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fb-b7c2-79d8980e6f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:href="tmc-20260930.xsd#tmc_GerradBarronAndErasCapitalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:to="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GerardBarronMember_01a15e28-38b3-71d5-bed4-8c104fbc80f9" xlink:href="tmc-20260930.xsd#tmc_GerardBarronMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:to="loc_tmc_GerardBarronMember_01a15e28-38b3-71d5-bed4-8c104fbc80f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ErasCapitalLlcMember_01a15e28-38b3-71ad-bb74-698c6a0cf9c6" xlink:href="tmc-20260930.xsd#tmc_ErasCapitalLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:to="loc_tmc_ErasCapitalLlcMember_01a15e28-38b3-71ad-bb74-698c6a0cf9c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7c11-91a7-06911bd441a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7c11-91a7-06911bd441a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a15e28-38b3-7e99-941b-07a8df90f4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:to="loc_us-gaap_LineOfCreditMember_01a15e28-38b3-7e99-941b-07a8df90f4ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-76c0-9ef1-b6e84de22286_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:to="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-76c0-9ef1-b6e84de22286_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:to="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a15e28-38b3-7210-b24c-725cdd791c71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:to="loc_us-gaap_RelatedPartyMember_01a15e28-38b3-7210-b24c-725cdd791c71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_01a1cc24-f894-7bf4-81fc-124e4df3f8d8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:to="loc_srt_DirectorMember_01a1cc24-f894-7bf4-81fc-124e4df3f8d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a15e75-388a-7726-b47e-8de436959a7f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a15e75-388a-7726-b47e-8de436959a7f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a1b208-8dea-741b-bd3e-33554d4a2cf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a1b208-8dea-741b-bd3e-33554d4a2cf3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate_01a1b208-8dea-7d55-9879-f76008895bee" xlink:href="tmc-20260930.xsd#tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate_01a1b208-8dea-7d55-9879-f76008895bee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a1b208-8dea-7642-9bd3-93de054f7536" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a1b208-8dea-7642-9bd3-93de054f7536" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity_01a1b208-8dea-78b3-b004-bdad3e82fed7" xlink:href="tmc-20260930.xsd#tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity_01a1b208-8dea-78b3-b004-bdad3e82fed7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a1b208-8dea-7ad2-987a-43015e3c35e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a1b208-8dea-7ad2-987a-43015e3c35e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfRelatedPartyDebt_01a1b208-a4c4-7931-ab4a-c611556b1ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfRelatedPartyDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_RepaymentsOfRelatedPartyDebt_01a1b208-a4c4-7931-ab4a-c611556b1ddb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfDebt_01a1b208-a4c4-7ccf-8091-845f704b08f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromRepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfDebt_01a1b208-a4c4-7ccf-8091-845f704b08f3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a1b208-a4c4-7941-85ec-dbb4f8653b8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LongTermDebt_01a1b208-a4c4-7941-85ec-dbb4f8653b8e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-751d-8d84-e5306f2d5a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-751d-8d84-e5306f2d5a8d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-706d-a55c-aaffaa0bd8ee" xlink:href="tmc-20260930.xsd#tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-706d-a55c-aaffaa0bd8ee" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_01a1b208-a4c4-78b9-8ff7-18e9f867705a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_InterestExpenseDebt_01a1b208-a4c4-78b9-8ff7-18e9f867705a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_01a1b208-a4c4-7ce3-8408-2f293b0b6163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_01a1b208-a4c4-7ce3-8408-2f293b0b6163" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RepaymentsOfInterestLineOfCredit_01a1b208-a4c4-7d2c-bf96-556b012b7ff5" xlink:href="tmc-20260930.xsd#tmc_RepaymentsOfInterestLineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_RepaymentsOfInterestLineOfCredit_01a1b208-a4c4-7d2c-bf96-556b012b7ff5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_01a1b208-a4c4-7432-b245-8f3d19c6eabf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProfessionalFees_01a1b208-a4c4-7432-b245-8f3d19c6eabf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LegalFees_01a1cc23-d067-7abf-929d-db3010735898" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LegalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LegalFees_01a1cc23-d067-7abf-929d-db3010735898" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/RelatedPartyTransactionsDetails_1" xlink:type="simple" xlink:href="tmc-20260930.xsd#RelatedPartyTransactionsDetails_1"/>
  <link:definitionLink xlink:role="http://tmc.com/role/RelatedPartyTransactionsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fb-b7c2-79d8980e6f99_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fb-b7c2-79d8980e6f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a15e28-38b3-75fb-b7c2-79d8980e6f99" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:href="tmc-20260930.xsd#tmc_GerradBarronAndErasCapitalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a15e28-38b3-75fc-b54e-48cf542eedf8" xlink:to="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_GerardBarronMember_01a15e28-38b3-71d5-bed4-8c104fbc80f9" xlink:href="tmc-20260930.xsd#tmc_GerardBarronMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:to="loc_tmc_GerardBarronMember_01a15e28-38b3-71d5-bed4-8c104fbc80f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ErasCapitalLlcMember_01a15e28-38b3-71ad-bb74-698c6a0cf9c6" xlink:href="tmc-20260930.xsd#tmc_ErasCapitalLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_tmc_GerradBarronAndErasCapitalLLCMember_01a15e28-38b3-7e1c-a8bf-4899a2bd7dac" xlink:to="loc_tmc_ErasCapitalLlcMember_01a15e28-38b3-71ad-bb74-698c6a0cf9c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7c11-91a7-06911bd441a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7c11-91a7-06911bd441a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a15e28-38b3-7c11-91a7-06911bd441a0" xlink:to="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a15e28-38b3-7e99-941b-07a8df90f4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a15e28-38b3-7350-8a65-5d80eb22622e" xlink:to="loc_us-gaap_LineOfCreditMember_01a15e28-38b3-7e99-941b-07a8df90f4ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a0817f-1eb9-780a-ae7f-e3de979f83e9" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-76c0-9ef1-b6e84de22286_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:to="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-76c0-9ef1-b6e84de22286_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a15e28-38b3-76c0-9ef1-b6e84de22286" xlink:to="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_01a15e28-38b3-7210-b24c-725cdd791c71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:to="loc_us-gaap_RelatedPartyMember_01a15e28-38b3-7210-b24c-725cdd791c71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_01a1cc24-f894-7bf4-81fc-124e4df3f8d8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a15e28-38b3-7501-b24f-5e2f2108d74c" xlink:to="loc_srt_DirectorMember_01a1cc24-f894-7bf4-81fc-124e4df3f8d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a1b208-8dea-741b-bd3e-33554d4a2cf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a1b208-8dea-741b-bd3e-33554d4a2cf3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate_01a1b208-8dea-7d55-9879-f76008895bee" xlink:href="tmc-20260930.xsd#tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_DebtInstrumentNumberOfDaysAverageConsideredForBasisSpreadOnVariableRate_01a1b208-8dea-7d55-9879-f76008895bee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a1b208-8dea-7642-9bd3-93de054f7536" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_01a1b208-8dea-7642-9bd3-93de054f7536" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity_01a1b208-8dea-78b3-b004-bdad3e82fed7" xlink:href="tmc-20260930.xsd#tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_DebtInstrumentVoluntaryInterestPaidInKindAtMaturity_01a1b208-8dea-78b3-b004-bdad3e82fed7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a1b208-8dea-7ad2-987a-43015e3c35e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a1b208-8dea-7ad2-987a-43015e3c35e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfRelatedPartyDebt_01a1b208-a4c4-7931-ab4a-c611556b1ddb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfRelatedPartyDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_RepaymentsOfRelatedPartyDebt_01a1b208-a4c4-7931-ab4a-c611556b1ddb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfDebt_01a1b208-a4c4-7ccf-8091-845f704b08f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromRepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfDebt_01a1b208-a4c4-7ccf-8091-845f704b08f3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a1b208-a4c4-7941-85ec-dbb4f8653b8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LongTermDebt_01a1b208-a4c4-7941-85ec-dbb4f8653b8e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-751d-8d84-e5306f2d5a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-751d-8d84-e5306f2d5a8d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-706d-a55c-aaffaa0bd8ee" xlink:href="tmc-20260930.xsd#tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_PaymentOfLineOfCreditFacilityCommitmentFeeAmount_01a1b208-a4c4-706d-a55c-aaffaa0bd8ee" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_01a1b208-a4c4-78b9-8ff7-18e9f867705a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_InterestExpenseDebt_01a1b208-a4c4-78b9-8ff7-18e9f867705a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_01a1b208-a4c4-7ce3-8408-2f293b0b6163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_01a1b208-a4c4-7ce3-8408-2f293b0b6163" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_RepaymentsOfInterestLineOfCredit_01a1b208-a4c4-7d2c-bf96-556b012b7ff5" xlink:href="tmc-20260930.xsd#tmc_RepaymentsOfInterestLineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_tmc_RepaymentsOfInterestLineOfCredit_01a1b208-a4c4-7d2c-bf96-556b012b7ff5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_01a1b208-a4c4-7432-b245-8f3d19c6eabf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_ProfessionalFees_01a1b208-a4c4-7432-b245-8f3d19c6eabf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LegalFees_01a1cc23-d067-7abf-929d-db3010735898" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LegalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a0817f-1eb9-7f27-a883-a1bec8b02070" xlink:to="loc_us-gaap_LegalFees_01a1cc23-d067-7abf-929d-db3010735898" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/ContingentLiabilitiesDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#ContingentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/ContingentLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_01a0817f-1eba-74aa-b963-a81b63178bae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_01a0817f-1eb9-7cb4-8c8c-9736b73991ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a0817f-1eba-74aa-b963-a81b63178bae" xlink:to="loc_us-gaap_OtherCommitmentsTable_01a0817f-1eb9-7cb4-8c8c-9736b73991ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a0817f-1eb9-7432-9e23-d09af18b425a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_01a0817f-1eb9-7cb4-8c8c-9736b73991ef" xlink:to="loc_dei_LegalEntityAxis_01a0817f-1eb9-7432-9e23-d09af18b425a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a0817f-1eb9-7432-9e23-d09af18b425a_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a0817f-1eb9-7432-9e23-d09af18b425a" xlink:to="loc_dei_EntityDomain_01a0817f-1eb9-7432-9e23-d09af18b425a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a0817f-1eb9-796f-995c-01f78f5ee706" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a0817f-1eb9-7432-9e23-d09af18b425a" xlink:to="loc_dei_EntityDomain_01a0817f-1eb9-796f-995c-01f78f5ee706" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-733d-98f7-88469708df59" xlink:href="tmc-20260930.xsd#tmc_NauruOceanResourcesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a0817f-1eb9-796f-995c-01f78f5ee706" xlink:to="loc_tmc_NauruOceanResourcesIncMember_01a0817f-1eb9-733d-98f7-88469708df59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TongaOffshoreMiningLimitedMember_01a0817f-1eb9-7124-92ee-27034d367d5a" xlink:href="tmc-20260930.xsd#tmc_TongaOffshoreMiningLimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a0817f-1eb9-796f-995c-01f78f5ee706" xlink:to="loc_tmc_TongaOffshoreMiningLimitedMember_01a0817f-1eb9-7124-92ee-27034d367d5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_01a0817f-1eb9-7cb4-8c8c-9736b73991ef" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7337-b391-d134fbd50202" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a0817f-1eb9-7aa0-8891-31ec36ce3cb5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7337-b391-d134fbd50202" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_NoriExplorationContractMember_01a0817f-1eb9-7403-b77a-8a6abe916de6" xlink:href="tmc-20260930.xsd#tmc_NoriExplorationContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7337-b391-d134fbd50202" xlink:to="loc_tmc_NoriExplorationContractMember_01a0817f-1eb9-7403-b77a-8a6abe916de6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_TongaOffshoreMiningLimitedExplorationContractMember_01a0817f-1eb9-7286-8b7a-abfdd78afc9d" xlink:href="tmc-20260930.xsd#tmc_TongaOffshoreMiningLimitedExplorationContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a0817f-1eb9-7337-b391-d134fbd50202" xlink:to="loc_tmc_TongaOffshoreMiningLimitedExplorationContractMember_01a0817f-1eb9-7286-8b7a-abfdd78afc9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_01a1b347-2f2d-7cf4-aab3-764703a76829" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_01a0817f-1eb9-7cb4-8c8c-9736b73991ef" xlink:to="loc_srt_StatementScenarioAxis_01a1b347-2f2d-7cf4-aab3-764703a76829" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1b347-2f2d-7cf4-aab3-764703a76829_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_01a1b347-2f2d-7cf4-aab3-764703a76829" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1b347-2f2d-7cf4-aab3-764703a76829_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_01a1b347-2f2d-7950-8069-229a2d56eb71" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_01a1b347-2f2d-7cf4-aab3-764703a76829" xlink:to="loc_srt_ScenarioUnspecifiedDomain_01a1b347-2f2d-7950-8069-229a2d56eb71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_01a1b347-4699-7ca6-85cb-4f224d0c469c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_01a1b347-2f2d-7950-8069-229a2d56eb71" xlink:to="loc_srt_ScenarioForecastMember_01a1b347-4699-7ca6-85cb-4f224d0c469c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_FiniteLivedIntangibleAssetContractExtensionPeriod_01a0817f-1eba-74d3-9ff7-da8378689348" xlink:href="tmc-20260930.xsd#tmc_FiniteLivedIntangibleAssetContractExtensionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a0817f-1eba-74aa-b963-a81b63178bae" xlink:to="loc_tmc_FiniteLivedIntangibleAssetContractExtensionPeriod_01a0817f-1eba-74d3-9ff7-da8378689348" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://tmc.com/role/SegmentedInformationDetails" xlink:type="simple" xlink:href="tmc-20260930.xsd#SegmentedInformationDetails"/>
  <link:definitionLink xlink:role="http://tmc.com/role/SegmentedInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a0817f-1eba-7caf-801b-b5a59c992cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a0817f-1eba-7caf-801b-b5a59c992cee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_01a0817f-1eba-7a04-ab56-270b177f5a39" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a0817f-1eba-7caf-801b-b5a59c992cee" xlink:to="loc_srt_StatementGeographicalAxis_01a0817f-1eba-7a04-ab56-270b177f5a39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7a04-ab56-270b177f5a39_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_01a0817f-1eba-7a04-ab56-270b177f5a39" xlink:to="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7a04-ab56-270b177f5a39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7540-aa19-2ee35b7783d3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_01a0817f-1eba-7a04-ab56-270b177f5a39" xlink:to="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7540-aa19-2ee35b7783d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_NR_01a0817f-1eba-7dca-8133-91e361948737" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_NR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7540-aa19-2ee35b7783d3" xlink:to="loc_country_NR_01a0817f-1eba-7dca-8133-91e361948737" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_SG_01a0817f-1eba-7079-93f4-9987df43314a" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_SG"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_01a0817f-1eba-7540-aa19-2ee35b7783d3" xlink:to="loc_country_SG_01a0817f-1eba-7079-93f4-9987df43314a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a0817f-1eba-7264-9890-cbbf90f71e9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a0817f-1eba-7caf-801b-b5a59c992cee" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a0817f-1eba-7264-9890-cbbf90f71e9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a0817f-1eba-7264-9890-cbbf90f71e9f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a0817f-1eba-7264-9890-cbbf90f71e9f" xlink:to="loc_us-gaap_SegmentDomain_01a0817f-1eba-7264-9890-cbbf90f71e9f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a0817f-1eba-798a-b0b1-12a928f208c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a0817f-1eba-7264-9890-cbbf90f71e9f" xlink:to="loc_us-gaap_SegmentDomain_01a0817f-1eba-798a-b0b1-12a928f208c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tmc_ReportableSegmentMember_01a0817f-1eba-7f1f-b488-572113846407" xlink:href="tmc-20260930.xsd#tmc_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a0817f-1eba-798a-b0b1-12a928f208c4" xlink:to="loc_tmc_ReportableSegmentMember_01a0817f-1eba-7f1f-b488-572113846407" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_01a0817f-1eba-7dfa-be51-cb0ffb11707f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:to="loc_us-gaap_NumberOfOperatingSegments_01a0817f-1eba-7dfa-be51-cb0ffb11707f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_01a0817f-1eba-71ad-921e-a61f12c5abbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:to="loc_us-gaap_NumberOfReportableSegments_01a0817f-1eba-71ad-921e-a61f12c5abbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_01a0817f-1eba-7a0f-97b0-9c3aa61a0974" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_01a0817f-1eba-7a0f-97b0-9c3aa61a0974" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a0817f-1eba-7b5b-8ca4-121904b478cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a0817f-1eba-7880-b239-4b3723f417c0" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a0817f-1eba-7b5b-8ca4-121904b478cd" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
