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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e8dc7-ef61-7782-9e17-6a6428baec48,g:28ca6551-5408-4d1c-8e53-9cbb3a8bbd98-->
<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://www.westport.com/role/CondensedConsolidatedInterimStatementsofShareholdersEquityunaudited" xlink:type="simple" xlink:href="wprt-20260630.xsd#CondensedConsolidatedInterimStatementsofShareholdersEquityunaudited"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/CondensedConsolidatedInterimStatementsofShareholdersEquityunaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e8dc7-f0ec-78d9-b095-5c564bfb362b" 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_019e8dc7-f0ec-7d89-8aac-e5db80a55985" 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_019e8dc7-f0ec-78d9-b095-5c564bfb362b" xlink:to="loc_us-gaap_StatementTable_019e8dc7-f0ec-7d89-8aac-e5db80a55985" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e8dc7-f0ec-71ce-b971-3928efa5ae23" 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_019e8dc7-f0ec-7d89-8aac-e5db80a55985" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e8dc7-f0ec-71ce-b971-3928efa5ae23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ec-71ce-b971-3928efa5ae23_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_019e8dc7-f0ec-71ce-b971-3928efa5ae23" xlink:to="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ec-71ce-b971-3928efa5ae23_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ec-7202-9b59-693cdeffd759" 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_019e8dc7-f0ec-71ce-b971-3928efa5ae23" xlink:to="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e8dc7-f0ec-793d-bffb-ba212f90e34a" 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_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:to="loc_us-gaap_CommonStockMember_019e8dc7-f0ec-793d-bffb-ba212f90e34a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_EquitySecuritiesOtherOneMember_019e8dc7-f0ec-79a3-b912-c33351bbe1be" xlink:href="wprt-20260630.xsd#wprt_EquitySecuritiesOtherOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:to="loc_wprt_EquitySecuritiesOtherOneMember_019e8dc7-f0ec-79a3-b912-c33351bbe1be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e8dc7-f0ec-7435-9c4c-ba98c3959c0f" 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_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e8dc7-f0ec-7435-9c4c-ba98c3959c0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e8dc7-f0ec-7db8-b695-9298a54ff5f4" 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_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:to="loc_us-gaap_RetainedEarningsMember_019e8dc7-f0ec-7db8-b695-9298a54ff5f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e8dc7-f0ec-73ca-a4db-ecd1984ec5bc" 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_019e8dc7-f0ec-7202-9b59-693cdeffd759" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019e8dc7-f0ec-73ca-a4db-ecd1984ec5bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" 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_019e8dc7-f0ec-78d9-b095-5c564bfb362b" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e8dc7-f0ec-77d5-9f35-22b93bf2202b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019e8dc7-f0ec-77d5-9f35-22b93bf2202b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e8dc7-f0ec-7bed-a8d6-0f539f7e4e5f" 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_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_StockholdersEquity_019e8dc7-f0ec-7bed-a8d6-0f539f7e4e5f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e8dc7-f0ec-72a0-95a8-c8d4f4c7c196" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e8dc7-f0ec-72a0-95a8-c8d4f4c7c196" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019e8dc7-f0ec-7d25-9aad-427c4c67cca8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019e8dc7-f0ec-7d25-9aad-427c4c67cca8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8f88-b913-7714-9113-164253cc9c29" 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_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019f8f88-b913-7714-9113-164253cc9c29" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f8f89-511c-78e1-ba2e-1ab2b0114c6f" 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_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019f8f89-511c-78e1-ba2e-1ab2b0114c6f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e8dc7-f0ec-742f-ae7d-19a929fd079c" 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_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019e8dc7-f0ec-742f-ae7d-19a929fd079c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e8dc7-f0ec-7421-8cc9-e7dff7897b09" 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_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_NetIncomeLoss_019e8dc7-f0ec-7421-8cc9-e7dff7897b09" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e8dc7-f0ec-776b-b71a-06313447408a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e8dc7-f0ec-7cad-a59f-6440d4b5cd54" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019e8dc7-f0ec-776b-b71a-06313447408a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019e8dc7-f0ec-7fc2-bcda-629ac63d3165" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e8dc7-f0ec-7fb6-afc7-02552080f0dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LiquidityandgoingconcernDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LiquidityandgoingconcernDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LiquidityandgoingconcernDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fa3cf-177b-782c-aeae-98927794f4a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_DebtInstrumentTable_019fa3cf-177b-782c-aeae-98927794f4a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fa3cf-177b-7aac-9c7c-aeb3461bee2e" 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_DebtInstrumentTable_019fa3cf-177b-782c-aeae-98927794f4a5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fa3cf-177b-7aac-9c7c-aeb3461bee2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fa3cf-177b-7aac-9c7c-aeb3461bee2e_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_019fa3cf-177b-7aac-9c7c-aeb3461bee2e" xlink:to="loc_us-gaap_EquityComponentDomain_019fa3cf-177b-7aac-9c7c-aeb3461bee2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fa3cf-177b-7590-a78b-96183c130cbb" 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_019fa3cf-177b-7aac-9c7c-aeb3461bee2e" xlink:to="loc_us-gaap_EquityComponentDomain_019fa3cf-177b-7590-a78b-96183c130cbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fa3cf-177b-70cb-ac5a-b1468ae02e49" 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_019fa3cf-177b-7590-a78b-96183c130cbb" xlink:to="loc_us-gaap_CommonStockMember_019fa3cf-177b-70cb-ac5a-b1468ae02e49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa3cf-177b-7d1f-b542-c3321a263b60" 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_DebtInstrumentTable_019fa3cf-177b-782c-aeae-98927794f4a5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fa3cf-177b-7d1f-b542-c3321a263b60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-7d1f-b542-c3321a263b60_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_019fa3cf-177b-7d1f-b542-c3321a263b60" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-7d1f-b542-c3321a263b60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-76c1-a461-cf7ce95fd0ef" 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_019fa3cf-177b-7d1f-b542-c3321a263b60" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-76c1-a461-cf7ce95fd0ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_PreFundedWarrantsMember_019fa3cf-177b-712e-a8df-57594a0a53a3" xlink:href="wprt-20260630.xsd#wprt_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-76c1-a461-cf7ce95fd0ef" xlink:to="loc_wprt_PreFundedWarrantsMember_019fa3cf-177b-712e-a8df-57594a0a53a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CommonWarrantsMember_019fa3cf-177b-7968-a19c-527e631ee60c" xlink:href="wprt-20260630.xsd#wprt_CommonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fa3cf-177b-76c1-a461-cf7ce95fd0ef" xlink:to="loc_wprt_CommonWarrantsMember_019fa3cf-177b-7968-a19c-527e631ee60c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019fa3cf-177b-7077-af87-7b6f4a0f321a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_OperatingIncomeLoss_019fa3cf-177b-7077-af87-7b6f4a0f321a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_019fa3cf-177b-7b21-82d9-1f4e027e539c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_019fa3cf-177b-7b21-82d9-1f4e027e539c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019fa3cf-177b-73a7-b62a-fa99724ae577" 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_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019fa3cf-177b-73a7-b62a-fa99724ae577" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_019fa3cf-177b-7201-9f36-e83804f7a1cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_019fa3cf-177b-7201-9f36-e83804f7a1cc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DebtInstrumentCovenantMinimumCashRequirement_019fa3cf-177b-717b-a350-0c8ceda36dbc" xlink:href="wprt-20260630.xsd#wprt_DebtInstrumentCovenantMinimumCashRequirement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_wprt_DebtInstrumentCovenantMinimumCashRequirement_019fa3cf-177b-717b-a350-0c8ceda36dbc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_MaximumProceedsFromIssuanceOfProspectusEquity_019fa3cf-177b-7ed3-9612-45645a82e85f" xlink:href="wprt-20260630.xsd#wprt_MaximumProceedsFromIssuanceOfProspectusEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_wprt_MaximumProceedsFromIssuanceOfProspectusEquity_019fa3cf-177b-7ed3-9612-45645a82e85f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShelfProspectusEffectiveTerm_019fa3cf-177b-7151-97f9-d27e2920904b" xlink:href="wprt-20260630.xsd#wprt_ShelfProspectusEffectiveTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_wprt_ShelfProspectusEffectiveTerm_019fa3cf-177b-7151-97f9-d27e2920904b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa3cf-177b-7510-b7b5-b70302c46f5c" 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_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa3cf-177b-7510-b7b5-b70302c46f5c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fa3cf-177b-77c2-8892-894d53071539" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fa3cf-177b-7344-9e05-15d914bf5c80" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fa3cf-177b-77c2-8892-894d53071539" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/BasisofpreparationDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#BasisofpreparationDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/BasisofpreparationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:href="wprt-20260630.xsd#wprt_ScheduleOfForeignCurrencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ScheduleOfForeignCurrencyTable_019e8dc7-f0ec-7571-8343-111ca3f414d9" xlink:href="wprt-20260630.xsd#wprt_ScheduleOfForeignCurrencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:to="loc_wprt_ScheduleOfForeignCurrencyTable_019e8dc7-f0ec-7571-8343-111ca3f414d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_wprt_ScheduleOfForeignCurrencyTable_019e8dc7-f0ec-7571-8343-111ca3f414d9" xlink:to="loc_srt_CurrencyAxis_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c_default" xlink:href="https://xbrl.sec.gov/currency/2026/currency-2026.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c" xlink:to="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7f52-ad42-ef5e5cbc111b" xlink:href="https://xbrl.sec.gov/currency/2026/currency-2026.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_019e8dc7-f0ec-7763-bdc4-cbb7522c1a3c" xlink:to="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7f52-ad42-ef5e5cbc111b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CAD_019e8dc7-f0ec-7b72-a834-67a3c01c088e" xlink:href="https://xbrl.sec.gov/currency/2026/currency-2026.xsd#currency_CAD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7f52-ad42-ef5e5cbc111b" xlink:to="loc_currency_CAD_019e8dc7-f0ec-7b72-a834-67a3c01c088e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_EUR_019e8dc7-f0ec-7d27-891c-bbd9a19cfed1" xlink:href="https://xbrl.sec.gov/currency/2026/currency-2026.xsd#currency_EUR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7f52-ad42-ef5e5cbc111b" xlink:to="loc_currency_EUR_019e8dc7-f0ec-7d27-891c-bbd9a19cfed1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CNY_019e8dc7-f0ec-7170-8c42-b5f34ae1e238" xlink:href="https://xbrl.sec.gov/currency/2026/currency-2026.xsd#currency_CNY"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_019e8dc7-f0ec-7f52-ad42-ef5e5cbc111b" xlink:to="loc_currency_CNY_019e8dc7-f0ec-7170-8c42-b5f34ae1e238" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fee74-3e62-7f64-83c3-a37164fa01e4" 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_wprt_ScheduleOfForeignCurrencyTable_019e8dc7-f0ec-7571-8343-111ca3f414d9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fee74-3e62-7f64-83c3-a37164fa01e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee74-3e62-7f64-83c3-a37164fa01e4_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_019fee74-3e62-7f64-83c3-a37164fa01e4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee74-3e62-7f64-83c3-a37164fa01e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee74-3e62-7ee5-91fc-25aa23f89224" 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_019fee74-3e62-7f64-83c3-a37164fa01e4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee74-3e62-7ee5-91fc-25aa23f89224" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_PreFundedWarrantsMember_019fee74-3e62-706b-8bb6-584988c330e0" xlink:href="wprt-20260630.xsd#wprt_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee74-3e62-7ee5-91fc-25aa23f89224" xlink:to="loc_wprt_PreFundedWarrantsMember_019fee74-3e62-706b-8bb6-584988c330e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019fd4c0-7ee1-7a42-b646-44d0f3d398ab" 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_wprt_ScheduleOfForeignCurrencyTable_019e8dc7-f0ec-7571-8343-111ca3f414d9" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019fd4c0-7ee1-7a42-b646-44d0f3d398ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-7a42-b646-44d0f3d398ab_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_019fd4c0-7ee1-7a42-b646-44d0f3d398ab" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-7a42-b646-44d0f3d398ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" 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_019fd4c0-7ee1-7a42-b646-44d0f3d398ab" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_019fd4c0-7ee1-78a6-a871-0eba929d7424" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_019fd4c0-7ee1-78a6-a871-0eba929d7424" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fd4c0-7ee1-7e91-be3b-eb70c9ceb7cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fd4c0-7ee1-7e91-be3b-eb70c9ceb7cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019fd4c0-7ee1-7ff9-971f-dd70e06441d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019fd4c0-7ee1-7ff9-971f-dd70e06441d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fd4c0-7ee1-7482-8753-76c40ccfec03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fd4c0-7ee1-7482-8753-76c40ccfec03" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fd4c0-7ee1-7390-86bc-8ac988584db0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd4c0-7ee1-78f5-8957-8873cf814a72" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fd4c0-7ee1-7390-86bc-8ac988584db0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyExchangeRateTranslation1_019e8dc7-f0ec-75af-b01f-97f93bf431eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyExchangeRateTranslation1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:to="loc_us-gaap_ForeignCurrencyExchangeRateTranslation1_019e8dc7-f0ec-75af-b01f-97f93bf431eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_AverageForeignCurrencyExchangeRateTranslation1_019e8dc7-f0ec-7102-a36e-8e358184169d" xlink:href="wprt-20260630.xsd#wprt_AverageForeignCurrencyExchangeRateTranslation1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:to="loc_wprt_AverageForeignCurrencyExchangeRateTranslation1_019e8dc7-f0ec-7102-a36e-8e358184169d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fee74-3e62-7b41-a547-ef93188a07cd" 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_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fee74-3e62-7b41-a547-ef93188a07cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fd4c0-7ee1-79c6-a71e-55f52a0eaf1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_ScheduleOfForeignCurrencyLineItems_019e8dc7-f0ec-7755-9c41-b79a5e9d1c7f" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fd4c0-7ee1-79c6-a71e-55f52a0eaf1f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/DiscontinuedoperationsNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#DiscontinuedoperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/DiscontinuedoperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7765-8c40-c7a37bee6ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-7626-a529-2d6a4a6280f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7765-8c40-c7a37bee6ce3" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-7626-a529-2d6a4a6280f5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-7626-a529-2d6a4a6280f5" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b97-828b-ca5e4e61ab4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-723f-b18f-c6ba2ed7955e" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b97-828b-ca5e4e61ab4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-72d8-b683-f2f09d523b5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b97-828b-ca5e4e61ab4a" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-72d8-b683-f2f09d523b5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-7626-a529-2d6a4a6280f5" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-78b8-a927-18a10959b929" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7e44-8c24-9858aa1bbdaa" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-78b8-a927-18a10959b929" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_LightDutyMember_019e8dc7-f0ec-7007-b6e6-bde19d8fd8a6" xlink:href="wprt-20260630.xsd#wprt_LightDutyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-78b8-a927-18a10959b929" xlink:to="loc_wprt_LightDutyMember_019e8dc7-f0ec-7007-b6e6-bde19d8fd8a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019e8dc7-f0ec-798f-9155-dcf0abae9020" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7765-8c40-c7a37bee6ce3" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019e8dc7-f0ec-798f-9155-dcf0abae9020" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationEarnoutsMaximum_019e8dc7-f0ec-7a4a-95d9-9a57998ff4b9" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationEarnoutsMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7765-8c40-c7a37bee6ce3" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationEarnoutsMaximum_019e8dc7-f0ec-7a4a-95d9-9a57998ff4b9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/DiscontinuedoperationsRevenueandExpensesoftheDiscontinuedOperationsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#DiscontinuedoperationsRevenueandExpensesoftheDiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/DiscontinuedoperationsRevenueandExpensesoftheDiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-764f-ab0c-599aee2a37ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-764f-ab0c-599aee2a37ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7d28-b997-968ac89be3a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-764f-ab0c-599aee2a37ea" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7d28-b997-968ac89be3a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7d28-b997-968ac89be3a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7d28-b997-968ac89be3a0" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7d28-b997-968ac89be3a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7358-8439-c74be4267080" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7d28-b997-968ac89be3a0" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7358-8439-c74be4267080" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-7b35-bf51-34d0f978b2be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7358-8439-c74be4267080" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-7b35-bf51-34d0f978b2be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e8dc7-f0ec-764f-ab0c-599aee2a37ea" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-718d-9dd2-99bd7ac77562" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019e8dc7-f0ec-7c03-b536-0c6f04ce8f31" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-718d-9dd2-99bd7ac77562" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_LightDutyMember_019e8dc7-f0ec-73d9-8376-71b48c3bca77" xlink:href="wprt-20260630.xsd#wprt_LightDutyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019e8dc7-f0ec-718d-9dd2-99bd7ac77562" xlink:to="loc_wprt_LightDutyMember_019e8dc7-f0ec-73d9-8376-71b48c3bca77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019e8dc7-f0ec-7dfc-a9d2-fc5c8e1c04a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019e8dc7-f0ec-7dfc-a9d2-fc5c8e1c04a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019e8dc7-f0ec-7a4c-a5e8-b09411458056" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019e8dc7-f0ec-7a4c-a5e8-b09411458056" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_019e8dc7-f0ec-756b-b285-97e336875abe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_019e8dc7-f0ec-756b-b285-97e336875abe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationResearchAndDevelopmentExpense_019e8dc7-f0ec-70ba-9c19-5aa30b3de678" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationResearchAndDevelopmentExpense_019e8dc7-f0ec-70ba-9c19-5aa30b3de678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_019e8dc7-f0ec-7535-8b6b-3cf74825692b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_019e8dc7-f0ec-7535-8b6b-3cf74825692b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationSellingAndMarketingExpense_019e8dc7-f0ec-7e86-86b4-fda2e2411c39" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationSellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationSellingAndMarketingExpense_019e8dc7-f0ec-7e86-86b4-fda2e2411c39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationForeignExchangeGainLoss_019e8dc7-f0ec-79a9-921e-ca4dd74e5530" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationForeignExchangeGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationForeignExchangeGainLoss_019e8dc7-f0ec-79a9-921e-ca4dd74e5530" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_019e8dc7-f0ec-7b50-8471-bcbdf0cf3257" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_019e8dc7-f0ec-7b50-8471-bcbdf0cf3257" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_019e8dc7-f0ec-7d2d-9812-dd35f8b45983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_DisposalGroupIncludingDiscontinuedOperationOperatingExpensesAbstract_019e8dc7-f0ec-7cf3-9681-f1e5d988e754" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_019e8dc7-f0ec-7d2d-9812-dd35f8b45983" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_019e8dc7-f0ec-7114-8f75-11c812227877" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_019e8dc7-f0ec-7114-8f75-11c812227877" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationIncomeLossFromEquityMethodInvestments_019e8dc7-f0ec-73e7-9ac8-9e2065759d6a" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationIncomeLossFromEquityMethodInvestments_019e8dc7-f0ec-73e7-9ac8-9e2065759d6a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax_019f6fbd-faec-7494-b871-0fc43012cdfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DiscontinuedOperationProvisionForLossGainOnDisposalBeforeIncomeTax_019f6fbd-faec-7494-b871-0fc43012cdfe" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationImpairmentOfLongLivedAssets_019f6fbd-faec-799d-95b8-7ade05ba676d" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationImpairmentOfLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationImpairmentOfLongLivedAssets_019f6fbd-faec-799d-95b8-7ade05ba676d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense_019e8dc7-f0ec-7011-89d9-4fec3917e83b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense_019e8dc7-f0ec-7011-89d9-4fec3917e83b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationInterestAndOtherIncomeExpense_019e8dc7-f0ec-7b47-bf48-b88062ebce67" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationInterestAndOtherIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationInterestAndOtherIncomeExpense_019e8dc7-f0ec-7b47-bf48-b88062ebce67" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019e8dc7-f0ec-7c15-bf22-a5a0b56cd676" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019e8dc7-f0ec-7c15-bf22-a5a0b56cd676" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_019e8dc7-f0ec-7afd-a154-13d9697ab79c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_019e8dc7-f0ec-7afd-a154-13d9697ab79c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019e8dc7-f0ec-75b5-9d85-e26d658e1eaa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e8dc7-f0ec-7c87-a88d-1c2b4d39d943" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019e8dc7-f0ec-75b5-9d85-e26d658e1eaa" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/AccountsreceivableScheduleofAccountsReceivableDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#AccountsreceivableScheduleofAccountsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/AccountsreceivableScheduleofAccountsReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7682-869b-5070a3dc03cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7682-869b-5070a3dc03cb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ec-7634-8e50-704762e5dd8f" 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_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7682-869b-5070a3dc03cb" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ec-7634-8e50-704762e5dd8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7634-8e50-704762e5dd8f_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_019e8dc7-f0ec-7634-8e50-704762e5dd8f" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7634-8e50-704762e5dd8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7f5f-a004-d471e809dbdf" 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_019e8dc7-f0ec-7634-8e50-704762e5dd8f" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7f5f-a004-d471e809dbdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019e8dc7-f0ec-736c-8d8d-231e454afd3c" 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_019e8dc7-f0ec-7f5f-a004-d471e809dbdf" xlink:to="loc_us-gaap_RelatedPartyMember_019e8dc7-f0ec-736c-8d8d-231e454afd3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_TradeAccountsReceivable_019e8dc7-f0ec-7fe7-9b7f-99798568b723" xlink:href="wprt-20260630.xsd#wprt_TradeAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_wprt_TradeAccountsReceivable_019e8dc7-f0ec-7fe7-9b7f-99798568b723" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HoldbackReceivablesNetCurrent_019e8dc7-f0ec-72de-830e-63698559f8a9" xlink:href="wprt-20260630.xsd#wprt_HoldbackReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_wprt_HoldbackReceivablesNetCurrent_019e8dc7-f0ec-72de-830e-63698559f8a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivables_019e8dc7-f0ec-7f35-903b-32aedc3dc354" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_us-gaap_OtherReceivables_019e8dc7-f0ec-7f35-903b-32aedc3dc354" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivablesNetCurrent_019e8dc7-f0ec-72e1-ae27-94e95e739408" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_us-gaap_OtherReceivablesNetCurrent_019e8dc7-f0ec-72e1-ae27-94e95e739408" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019e8dc7-f0ec-7787-a3ea-996a3a6c3009" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019e8dc7-f0ec-7787-a3ea-996a3a6c3009" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019e8dc7-f0ec-7ad3-9a74-4db475a3befb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7e5a-b215-fbbd7c100f5f" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019e8dc7-f0ec-7ad3-9a74-4db475a3befb" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/AccountsreceivableNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#AccountsreceivableNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/AccountsreceivableNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7017-8f08-e7a9ce932e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7049-91c1-742f67505536" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7017-8f08-e7a9ce932e3d" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7049-91c1-742f67505536" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_019e8dc7-f0ec-7049-91c1-742f67505536" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b8f-ab5a-6906fe928678" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019e8dc7-f0ec-7622-9b7f-aeb20f35e70a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b8f-ab5a-6906fe928678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-7155-801f-afc81189b1f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019e8dc7-f0ec-7b8f-ab5a-6906fe928678" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019e8dc7-f0ec-7155-801f-afc81189b1f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DisposalGroupIncludingDiscontinuedOperationHeldInEscrow_019e8dc7-f0ec-7446-a76c-cf21d9e86f79" xlink:href="wprt-20260630.xsd#wprt_DisposalGroupIncludingDiscontinuedOperationHeldInEscrow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7017-8f08-e7a9ce932e3d" xlink:to="loc_wprt_DisposalGroupIncludingDiscontinuedOperationHeldInEscrow_019e8dc7-f0ec-7446-a76c-cf21d9e86f79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HoldbackReceivablesNetCurrent_019e8dc7-f0ec-740a-b93f-a913fe8682a2" xlink:href="wprt-20260630.xsd#wprt_HoldbackReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7017-8f08-e7a9ce932e3d" xlink:to="loc_wprt_HoldbackReceivablesNetCurrent_019e8dc7-f0ec-740a-b93f-a913fe8682a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ec-72d0-b1f8-1ff3b485d3c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_019e8dc7-f0ec-7017-8f08-e7a9ce932e3d" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ec-72d0-b1f8-1ff3b485d3c2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongterminvestmentsScheduleofInvestmentsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongterminvestmentsScheduleofInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongterminvestmentsScheduleofInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7df4-a64d-7c6b50fcea57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-709a-b37a-d0f9df15b286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7df4-a64d-7c6b50fcea57" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-709a-b37a-d0f9df15b286" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e8dc7-f0ec-7277-9b18-35d792ffbfc9" 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_ScheduleOfInvestmentsTable_019e8dc7-f0ec-709a-b37a-d0f9df15b286" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019e8dc7-f0ec-7277-9b18-35d792ffbfc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7277-9b18-35d792ffbfc9_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_019e8dc7-f0ec-7277-9b18-35d792ffbfc9" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7277-9b18-35d792ffbfc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7d9d-90f7-d1bd5c98bc3a" 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_019e8dc7-f0ec-7277-9b18-35d792ffbfc9" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7d9d-90f7-d1bd5c98bc3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraCanadaLPMember_019e8dc7-f0ec-7489-8434-c59292758552" xlink:href="wprt-20260630.xsd#wprt_CespiraCanadaLPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7d9d-90f7-d1bd5c98bc3a" xlink:to="loc_wprt_CespiraCanadaLPMember_019e8dc7-f0ec-7489-8434-c59292758552" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraSwedenABMember_019e8dc7-f0ec-7ee4-b8b9-79129c5d009a" xlink:href="wprt-20260630.xsd#wprt_CespiraSwedenABMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019e8dc7-f0ec-7d9d-90f7-d1bd5c98bc3a" xlink:to="loc_wprt_CespiraSwedenABMember_019e8dc7-f0ec-7ee4-b8b9-79129c5d009a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_019e8dc7-f0ec-7ef1-b6c2-cff6366220e6" 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_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7df4-a64d-7c6b50fcea57" xlink:to="loc_us-gaap_LongTermInvestments_019e8dc7-f0ec-7ef1-b6c2-cff6366220e6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongterminvestmentsMaximumExposureDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongterminvestmentsMaximumExposureDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongterminvestmentsMaximumExposureDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fb879-a2da-7251-9502-0eea67487ecf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019fb879-a2da-75ac-8403-1fa265480a47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fb879-a2da-7251-9502-0eea67487ecf" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019fb879-a2da-75ac-8403-1fa265480a47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fb879-a2da-7212-a5aa-c797e90e3fb5" 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_ScheduleOfInvestmentsTable_019fb879-a2da-75ac-8403-1fa265480a47" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019fb879-a2da-7212-a5aa-c797e90e3fb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fb879-a2da-7212-a5aa-c797e90e3fb5_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_019fb879-a2da-7212-a5aa-c797e90e3fb5" xlink:to="loc_us-gaap_RelatedPartyDomain_019fb879-a2da-7212-a5aa-c797e90e3fb5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019fb879-a2da-751c-b724-659ac443f327" 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_019fb879-a2da-7212-a5aa-c797e90e3fb5" xlink:to="loc_us-gaap_RelatedPartyDomain_019fb879-a2da-751c-b724-659ac443f327" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraMember_019fb879-a2da-755d-8550-3913fc380bdc" xlink:href="wprt-20260630.xsd#wprt_CespiraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019fb879-a2da-751c-b724-659ac443f327" xlink:to="loc_wprt_CespiraMember_019fb879-a2da-755d-8550-3913fc380bdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_019fb879-a2da-7443-829f-4064f1fbae02" 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_us-gaap_ScheduleOfInvestmentsLineItems_019fb879-a2da-7251-9502-0eea67487ecf" xlink:to="loc_us-gaap_LongTermInvestments_019fb879-a2da-7443-829f-4064f1fbae02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivablesNetCurrent_019fb879-a2da-7ce7-b5cb-d3f34589ed99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fb879-a2da-7251-9502-0eea67487ecf" xlink:to="loc_us-gaap_OtherReceivablesNetCurrent_019fb879-a2da-7ce7-b5cb-d3f34589ed99" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongterminvestmentsBalanceSheetDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongterminvestmentsBalanceSheetDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongterminvestmentsBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7f14-8cc5-6c11c68040e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7f14-8cc5-6c11c68040e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-72ba-a590-087d32c7c96f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7f14-8cc5-6c11c68040e0" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-72ba-a590-087d32c7c96f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-72ba-a590-087d32c7c96f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-72ba-a590-087d32c7c96f" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-72ba-a590-087d32c7c96f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7284-91da-7ec9f76a1428" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-72ba-a590-087d32c7c96f" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7284-91da-7ec9f76a1428" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraJointVentureMember_019e8dc7-f0ec-7dd5-9d58-7a36c51d0fbf" xlink:href="wprt-20260630.xsd#wprt_CespiraJointVentureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7284-91da-7ec9f76a1428" xlink:to="loc_wprt_CespiraJointVentureMember_019e8dc7-f0ec-7dd5-9d58-7a36c51d0fbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019e8dc7-f0ec-7997-aea0-91fac83f31f8" 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_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019e8dc7-f0ec-7997-aea0-91fac83f31f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019e8dc7-f0ec-77db-9627-b2aa8de518d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019e8dc7-f0ec-77db-9627-b2aa8de518d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019e8dc7-f0ec-7a60-ad1a-ded3d22cc305" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:to="loc_us-gaap_InventoryNet_019e8dc7-f0ec-7a60-ad1a-ded3d22cc305" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseCurrentAndNoncurrent_019e8dc7-f0ec-7a6b-a7dd-cdcf35dad758" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:to="loc_us-gaap_PrepaidExpenseCurrentAndNoncurrent_019e8dc7-f0ec-7a6b-a7dd-cdcf35dad758" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019e8dc7-f0ec-72d2-a0cf-52af78231cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019e8dc7-f0ec-744f-b698-a9ee317d8788" xlink:to="loc_us-gaap_AssetsCurrent_019e8dc7-f0ec-72d2-a0cf-52af78231cc0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8dc7-f0ec-728a-9fde-7c1b57c0dbcc" 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_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8dc7-f0ec-728a-9fde-7c1b57c0dbcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019e8dc7-f0ec-70a0-b4db-3dfbea8d8e82" 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_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019e8dc7-f0ec-70a0-b4db-3dfbea8d8e82" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019e8dc7-f0ec-7296-abfd-c52150e516d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019e8dc7-f0ec-7296-abfd-c52150e516d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019e8dc7-f0ec-702c-a01d-d10a55912014" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_Assets_019e8dc7-f0ec-702c-a01d-d10a55912014" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019e8dc7-f0ec-7ea4-af4e-e96e859756c9" 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_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019e8dc7-f0ec-7ea4-af4e-e96e859756c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_019e8dc7-f0ec-7151-853e-5e3a2d38673e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:to="loc_us-gaap_ShortTermBorrowings_019e8dc7-f0ec-7151-853e-5e3a2d38673e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019e8dc7-f0ec-7feb-b5e4-5a015d63a147" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019e8dc7-f0ec-7feb-b5e4-5a015d63a147" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019e8dc7-f0ec-7efe-bc3d-8d781caa482d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019e8dc7-f0ec-7d20-a01e-d77895614a9c" xlink:to="loc_us-gaap_LiabilitiesCurrent_019e8dc7-f0ec-7efe-bc3d-8d781caa482d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019e8dc7-f0ec-7e13-95e3-25a730d2c964" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019e8dc7-f0ec-7e13-95e3-25a730d2c964" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ContractProvisionNoncurrent_019e8dc7-f0ec-7483-b211-8455be8afee2" xlink:href="wprt-20260630.xsd#wprt_ContractProvisionNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_wprt_ContractProvisionNoncurrent_019e8dc7-f0ec-7483-b211-8455be8afee2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019e8dc7-f0ec-7c83-af2d-72c0e9216745" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_Liabilities_019e8dc7-f0ec-7c83-af2d-72c0e9216745" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNet_019e8dc7-f0ec-7f5b-a8dd-7b1a0636d5bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-7a58-83c0-f8497ba9afdc" xlink:to="loc_us-gaap_AssetsNet_019e8dc7-f0ec-7f5b-a8dd-7b1a0636d5bc" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongterminvestmentsIncomeStatementDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongterminvestmentsIncomeStatementDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongterminvestmentsIncomeStatementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7fb5-ae10-13ab26245f86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7fb5-ae10-13ab26245f86" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7fb5-ae10-13ab26245f86" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7b92-af48-ed236c81f8cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis_019e8dc7-f0ec-7ef5-92a6-8ec73e62b505" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7b92-af48-ed236c81f8cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraJointVentureMember_019e8dc7-f0ec-74ae-9128-9c7892e1a34d" xlink:href="wprt-20260630.xsd#wprt_CespiraJointVentureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019e8dc7-f0ec-7b92-af48-ed236c81f8cf" xlink:to="loc_wprt_CespiraJointVentureMember_019e8dc7-f0ec-74ae-9128-9c7892e1a34d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019e8dc7-f0ec-7fb5-ae10-13ab26245f86" xlink:to="loc_srt_ProductOrServiceAxis_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929" xlink:to="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-71f1-8b23-fecb7fd23f83" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e8dc7-f0ec-7942-b1fc-2ac4dd95b929" xlink:to="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-71f1-8b23-fecb7fd23f83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019e8dc7-f0ec-72d9-ae2f-313324398f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-71f1-8b23-fecb7fd23f83" xlink:to="loc_us-gaap_ProductMember_019e8dc7-f0ec-72d9-ae2f-313324398f5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_AftermarketMember_019fb87d-c1c6-7392-ab87-df3a91941231" xlink:href="wprt-20260630.xsd#wprt_AftermarketMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-71f1-8b23-fecb7fd23f83" xlink:to="loc_wprt_AftermarketMember_019fb87d-c1c6-7392-ab87-df3a91941231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_019e8dc7-f0ec-7e90-b4fd-fc9dbddf14b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e8dc7-f0ec-71f1-8b23-fecb7fd23f83" xlink:to="loc_us-gaap_ServiceMember_019e8dc7-f0ec-7e90-b4fd-fc9dbddf14b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8dc7-f0ec-71de-822c-c2565e50976d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8dc7-f0ec-71de-822c-c2565e50976d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019e8dc7-f0ec-7d7e-901c-c580602d62bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_CostOfRevenue_019e8dc7-f0ec-7d7e-901c-c580602d62bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019e8dc7-f0ec-79bc-a864-8a5ca058f0f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_GrossProfit_019e8dc7-f0ec-79bc-a864-8a5ca058f0f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e8dc7-f0ec-7330-bc9e-1ed43c63d444" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e8dc7-f0ec-7330-bc9e-1ed43c63d444" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e8dc7-f0ec-7d22-8768-6bbc817931c0" 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_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e8dc7-f0ec-7d22-8768-6bbc817931c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e8dc7-f0ec-763a-9702-69d3c6bf63dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e8dc7-f0ec-763a-9702-69d3c6bf63dd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019e8dc7-f0ec-7ea8-bee4-26e112cd06d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019e8dc7-f0ec-7ea8-bee4-26e112cd06d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_019e8dc7-f0ec-75df-b985-b5cf1b0db878" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_019e8dc7-f0ec-75df-b985-b5cf1b0db878" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019e8dc7-f0ec-7fa5-9339-78a6615cf0be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_019e8dc7-f0ec-7003-ae44-2d5b71b5972f" xlink:to="loc_us-gaap_CostsAndExpenses_019e8dc7-f0ec-7fa5-9339-78a6615cf0be" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e8dc7-f0ec-712b-a965-15fe69399433" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e8dc7-f0ec-712b-a965-15fe69399433" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ec-74e5-adef-07c75b548cdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ec-74e5-adef-07c75b548cdc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8dc7-f0ec-7f61-b751-87b266c00f29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8dc7-f0ec-7f61-b751-87b266c00f29" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e8dc7-f0ec-7d77-801e-1934fedf9c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e8dc7-f0ec-7d77-801e-1934fedf9c1b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_019e8dc7-f0ec-7f5f-b390-4734aa21a001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019e8dc7-f0ec-747f-b817-fa48ba654321" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_019e8dc7-f0ec-7f5f-b390-4734aa21a001" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/PropertyplantandequipmentDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#PropertyplantandequipmentDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/PropertyplantandequipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e8dc7-f0ec-71c9-a03a-38877004f31b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e8dc7-f0ec-7df7-aed8-52b3dcbee2c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e8dc7-f0ec-71c9-a03a-38877004f31b" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e8dc7-f0ec-7df7-aed8-52b3dcbee2c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e8dc7-f0ec-7df7-aed8-52b3dcbee2c5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e8dc7-f0ec-7143-83f6-fe0f9e99b0d3" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ComputerEquipmentAndSoftwareMember_019e8dc7-f0ec-7dc0-a031-340ed203d8e1" xlink:href="wprt-20260630.xsd#wprt_ComputerEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:to="loc_wprt_ComputerEquipmentAndSoftwareMember_019e8dc7-f0ec-7dc0-a031-340ed203d8e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019e8dc7-f0ec-7826-891b-067dd264dbb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019e8dc7-f0ec-7826-891b-067dd264dbb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_019e8dc7-f0ec-7b2f-9f40-ab964013538d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_019e8dc7-f0ec-7b2f-9f40-ab964013538d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019e8dc7-f0ec-7a01-b6a8-a6eb254d5949" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e8dc7-f0ec-7404-a5ff-6937637f65d0" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019e8dc7-f0ec-7a01-b6a8-a6eb254d5949" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019e8dc7-f0ec-71a7-a417-e5c7a73522a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e8dc7-f0ec-71c9-a03a-38877004f31b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019e8dc7-f0ec-71a7-a417-e5c7a73522a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e8dc7-f0ec-781a-a774-56c8490e7aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e8dc7-f0ec-71c9-a03a-38877004f31b" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e8dc7-f0ec-781a-a774-56c8490e7aa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8dc7-f0ec-7f92-8f1c-866f26c61788" 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_PropertyPlantAndEquipmentLineItems_019e8dc7-f0ec-71c9-a03a-38877004f31b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e8dc7-f0ec-7f92-8f1c-866f26c61788" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/AccountspayableandaccruedliabilitiesDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#AccountspayableandaccruedliabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/AccountspayableandaccruedliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShortTermDebtTable_019e8dc7-f0ec-76fd-945d-6dd15e284adc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShortTermDebtTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_ScheduleOfShortTermDebtTable_019e8dc7-f0ec-76fd-945d-6dd15e284adc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d" 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_ScheduleOfShortTermDebtTable_019e8dc7-f0ec-76fd-945d-6dd15e284adc" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d_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_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7fce-abd0-f15c069af960" 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_019e8dc7-f0ec-7ec4-a1f7-69674d3a7f2d" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ec-7fce-abd0-f15c069af960" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019e8dc7-f0ec-7d5f-93c3-30732295004f" 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_019e8dc7-f0ec-7fce-abd0-f15c069af960" xlink:to="loc_us-gaap_RelatedPartyMember_019e8dc7-f0ec-7d5f-93c3-30732295004f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableTradeCurrent_019e8dc7-f0ec-744a-aa09-ebbb307ae34c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableTradeCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_AccountsPayableTradeCurrent_019e8dc7-f0ec-744a-aa09-ebbb307ae34c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019e8dc7-f0ec-7e8b-bf7a-3ddcc6e92037" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_019e8dc7-f0ec-7e8b-bf7a-3ddcc6e92037" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_019e8dc7-f0ec-70c4-9aa1-068170a01af0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_019e8dc7-f0ec-70c4-9aa1-068170a01af0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e8dc7-f0ec-7d87-8677-f52f5a503e6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_019e8dc7-f0ec-7d87-8677-f52f5a503e6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNotesPayableCurrent_019e8dc7-f0ec-7218-bec1-02ef23ec4cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNotesPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_OtherNotesPayableCurrent_019e8dc7-f0ec-7218-bec1-02ef23ec4cd5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019e8dc7-f0ec-7623-8f08-6d175c302cc0" 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_us-gaap_ShortTermDebtLineItems_019e8dc7-f0ec-7b41-905a-7290884a4d4f" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019e8dc7-f0ec-7623-8f08-6d175c302cc0" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongtermdebtTermLoanFacilitiesDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongtermdebtTermLoanFacilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongtermdebtTermLoanFacilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7795-b49a-00ced0599103" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-78f0-8d63-dcfdabd3d25e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7795-b49a-00ced0599103" xlink:to="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-78f0-8d63-dcfdabd3d25e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0" 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_DebtInstrumentTable_019e8dc7-f0ec-78f0-8d63-dcfdabd3d25e" xlink:to="loc_us-gaap_CreditFacilityAxis_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0_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_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0" xlink:to="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-75c1-bbf6-af3b4b36b027" 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_019e8dc7-f0ec-7268-a09a-5c0f4a2052c0" xlink:to="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-75c1-bbf6-af3b4b36b027" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e8dc7-f0ec-7d24-8cdd-08d7913d42b0" 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_CreditFacilityDomain_019e8dc7-f0ec-75c1-bbf6-af3b4b36b027" xlink:to="loc_us-gaap_SecuredDebtMember_019e8dc7-f0ec-7d24-8cdd-08d7913d42b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-78f0-8d63-dcfdabd3d25e" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-7056-a903-59bec37784cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-7ce4-af9d-7f076dec2ce9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-7056-a903-59bec37784cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_EDCLoanMember_019e8dc7-f0ec-71ea-a6eb-39f13801e44c" xlink:href="wprt-20260630.xsd#wprt_EDCLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-7056-a903-59bec37784cb" xlink:to="loc_wprt_EDCLoanMember_019e8dc7-f0ec-71ea-a6eb-39f13801e44c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019e8dc7-f0ec-7af5-bc48-045ab0ba2288" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7795-b49a-00ced0599103" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019e8dc7-f0ec-7af5-bc48-045ab0ba2288" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_019e8dc7-f0ec-7f8a-ae8e-03c179c6698e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7795-b49a-00ced0599103" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_019e8dc7-f0ec-7f8a-ae8e-03c179c6698e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019e8dc7-f0ec-70b9-863c-969764be2440" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7795-b49a-00ced0599103" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019e8dc7-f0ec-70b9-863c-969764be2440" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/LongtermdebtNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#LongtermdebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/LongtermdebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7a31-8d32-d1e1aac72966" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-7727-b7ab-ff66e3aa1070" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7a31-8d32-d1e1aac72966" xlink:to="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-7727-b7ab-ff66e3aa1070" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e8dc7-f0ec-75e8-b960-5858b9d96562" 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_DebtInstrumentTable_019e8dc7-f0ec-7727-b7ab-ff66e3aa1070" xlink:to="loc_us-gaap_CreditFacilityAxis_019e8dc7-f0ec-75e8-b960-5858b9d96562" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-75e8-b960-5858b9d96562_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_019e8dc7-f0ec-75e8-b960-5858b9d96562" xlink:to="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-75e8-b960-5858b9d96562_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-7dc4-a4dd-b9b56986f99a" 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_019e8dc7-f0ec-75e8-b960-5858b9d96562" xlink:to="loc_us-gaap_CreditFacilityDomain_019e8dc7-f0ec-7dc4-a4dd-b9b56986f99a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e8dc7-f0ec-7546-ba65-076c13cf711b" 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_CreditFacilityDomain_019e8dc7-f0ec-7dc4-a4dd-b9b56986f99a" xlink:to="loc_us-gaap_SecuredDebtMember_019e8dc7-f0ec-7546-ba65-076c13cf711b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-729b-9d9e-3d77150f12eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019e8dc7-f0ec-7727-b7ab-ff66e3aa1070" xlink:to="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-729b-9d9e-3d77150f12eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-729b-9d9e-3d77150f12eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-729b-9d9e-3d77150f12eb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-729b-9d9e-3d77150f12eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-73f5-b9d6-fd6c807ec25e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019e8dc7-f0ec-729b-9d9e-3d77150f12eb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-73f5-b9d6-fd6c807ec25e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_EDCLoanMember_019e8dc7-f0ec-750b-9949-2dba529fc67f" xlink:href="wprt-20260630.xsd#wprt_EDCLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019e8dc7-f0ec-73f5-b9d6-fd6c807ec25e" xlink:to="loc_wprt_EDCLoanMember_019e8dc7-f0ec-750b-9949-2dba529fc67f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019e8dc7-f0ec-7b05-8627-65e0623fd04d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7a31-8d32-d1e1aac72966" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019e8dc7-f0ec-7b05-8627-65e0623fd04d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_DebtInstrumentCovenantMinimumCashRequirement_019f93fd-d058-7265-a439-71a43c97a9b6" xlink:href="wprt-20260630.xsd#wprt_DebtInstrumentCovenantMinimumCashRequirement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019e8dc7-f0ec-7a31-8d32-d1e1aac72966" xlink:to="loc_wprt_DebtInstrumentCovenantMinimumCashRequirement_019f93fd-d058-7265-a439-71a43c97a9b6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/WarrantliabilitiesNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#WarrantliabilitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/WarrantliabilitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" 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_019f7049-54d9-7d63-9fba-4aa61416fb44" 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_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019f7049-54d9-7d63-9fba-4aa61416fb44" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fb856-650e-73c5-af8f-8fdf021884c7" 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_ClassOfWarrantOrRightTable_019f7049-54d9-7d63-9fba-4aa61416fb44" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fb856-650e-73c5-af8f-8fdf021884c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fb856-650e-73c5-af8f-8fdf021884c7_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_019fb856-650e-73c5-af8f-8fdf021884c7" xlink:to="loc_us-gaap_EquityComponentDomain_019fb856-650e-73c5-af8f-8fdf021884c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fb856-650e-7566-9b42-af9a32a34099" 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_019fb856-650e-73c5-af8f-8fdf021884c7" xlink:to="loc_us-gaap_EquityComponentDomain_019fb856-650e-7566-9b42-af9a32a34099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fb856-650e-76a0-b384-4db70a93ac4b" 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_019fb856-650e-7566-9b42-af9a32a34099" xlink:to="loc_us-gaap_CommonStockMember_019fb856-650e-76a0-b384-4db70a93ac4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019f7049-54d9-702a-b271-38ddcd3c7019" 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_019f7049-54d9-7d63-9fba-4aa61416fb44" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019f7049-54d9-702a-b271-38ddcd3c7019" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-702a-b271-38ddcd3c7019_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_019f7049-54d9-702a-b271-38ddcd3c7019" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-702a-b271-38ddcd3c7019_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-7d6c-b184-cdf5a54cc6f8" 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_019f7049-54d9-702a-b271-38ddcd3c7019" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-7d6c-b184-cdf5a54cc6f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CommonWarrantsMember_019f7049-54d9-7ce4-9391-a18c9a3b2ef0" xlink:href="wprt-20260630.xsd#wprt_CommonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-7d6c-b184-cdf5a54cc6f8" xlink:to="loc_wprt_CommonWarrantsMember_019f7049-54d9-7ce4-9391-a18c9a3b2ef0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_PreFundedWarrantsMember_019fb856-650e-71dd-90b0-7bf05290ab1c" xlink:href="wprt-20260630.xsd#wprt_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019f7049-54d9-7d6c-b184-cdf5a54cc6f8" xlink:to="loc_wprt_PreFundedWarrantsMember_019fb856-650e-71dd-90b0-7bf05290ab1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fb856-650e-7bb8-90f7-2e9e18e17adf" 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_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fb856-650e-7bb8-90f7-2e9e18e17adf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fb856-650e-7275-9e3d-57e587d9780f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_019fb856-650e-7275-9e3d-57e587d9780f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ProceedsFromIssuanceOfCommonStockWarrantsAndPreFundedWarrants_019fb856-650e-71e5-af88-338316737a64" xlink:href="wprt-20260630.xsd#wprt_ProceedsFromIssuanceOfCommonStockWarrantsAndPreFundedWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_wprt_ProceedsFromIssuanceOfCommonStockWarrantsAndPreFundedWarrants_019fb856-650e-71e5-af88-338316737a64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fb890-0094-7a12-9246-6c99905327a0" 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_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_019fb890-0094-7a12-9246-6c99905327a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstanding_019fb856-650e-7b25-8ec2-3cb01bfbb574" 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_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_WarrantsAndRightsOutstanding_019fb856-650e-7b25-8ec2-3cb01bfbb574" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019fb856-650e-74a0-ab75-a494aa1d8b47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_019fb856-650e-74a0-ab75-a494aa1d8b47" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_019fd4c5-0024-7309-9082-3fe843a40d44" 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_us-gaap_ClassOfWarrantOrRightLineItems_019f7049-54d9-7bef-a2dc-77d36c563dbe" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_019fd4c5-0024-7309-9082-3fe843a40d44" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/WarrantliabilitiesScheduleofShareBasedPaymentAwardStockOptionsValuationAssumptionsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#WarrantliabilitiesScheduleofShareBasedPaymentAwardStockOptionsValuationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/WarrantliabilitiesScheduleofShareBasedPaymentAwardStockOptionsValuationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fa3b0-721f-7476-a826-500551cf7b95" 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_019fa3b0-721f-76e1-b702-828c6230be46" 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_019fa3b0-721f-7476-a826-500551cf7b95" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019fa3b0-721f-76e1-b702-828c6230be46" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019fa3b0-721f-7387-8032-094d7dd60117" 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_us-gaap_ClassOfWarrantOrRightTable_019fa3b0-721f-76e1-b702-828c6230be46" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019fa3b0-721f-7387-8032-094d7dd60117" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7387-8032-094d7dd60117_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_019fa3b0-721f-7387-8032-094d7dd60117" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7387-8032-094d7dd60117_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" 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_019fa3b0-721f-7387-8032-094d7dd60117" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fd8c2-6c3d-7c1c-932d-240021de5778" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019fd8c2-6c3d-7c1c-932d-240021de5778" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_019fa3b0-721f-74a5-a788-d976c7a729d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_019fa3b0-721f-74a5-a788-d976c7a729d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fa3b0-721f-79fb-8f6a-863b0d1c923d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019fa3b0-721f-79fb-8f6a-863b0d1c923d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_019fa3b0-721f-718d-a453-a33e6789cb61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_019fa3b0-721f-718d-a453-a33e6789cb61" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fa3b0-721f-7533-bfa3-a433c2d486e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fa3b0-721f-7718-8c53-ce21f06856d0" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_019fa3b0-721f-7533-bfa3-a433c2d486e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fa3b0-721f-72ff-a96d-abb7f3874728" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fa3b0-721f-7476-a826-500551cf7b95" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_019fa3b0-721f-72ff-a96d-abb7f3874728" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/WarrantliabilitiesScheduleofDerivativeLiabilitiesatFairValueDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#WarrantliabilitiesScheduleofDerivativeLiabilitiesatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/WarrantliabilitiesScheduleofDerivativeLiabilitiesatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fb85e-3c4e-773c-a462-b004cfa5f7b4" 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_019fb85e-3c4e-7158-9d3c-518cd6a2008f" 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_019fb85e-3c4e-773c-a462-b004cfa5f7b4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019fb85e-3c4e-7158-9d3c-518cd6a2008f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019fb85e-3c4e-7f18-a701-7f6f28f592bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019fb85e-3c4e-7158-9d3c-518cd6a2008f" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019fb85e-3c4e-7f18-a701-7f6f28f592bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fb85e-3c4e-7f18-a701-7f6f28f592bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fb85e-3c4e-7f18-a701-7f6f28f592bf" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fb85e-3c4e-7f18-a701-7f6f28f592bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fb85e-3c4e-7388-951e-08a24953be81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fb85e-3c4e-7f18-a701-7f6f28f592bf" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fb85e-3c4e-7388-951e-08a24953be81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019fb85e-3c4e-7250-8deb-8693d17fef44" 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_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fb85e-3c4e-7388-951e-08a24953be81" xlink:to="loc_us-gaap_WarrantMember_019fb85e-3c4e-7250-8deb-8693d17fef44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019fee7a-91d6-73ab-98a9-7ea5a33bb103" 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_019fb85e-3c4e-7158-9d3c-518cd6a2008f" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019fee7a-91d6-73ab-98a9-7ea5a33bb103" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-73ab-98a9-7ea5a33bb103_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_019fee7a-91d6-73ab-98a9-7ea5a33bb103" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-73ab-98a9-7ea5a33bb103_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-7633-bd2c-98a3eccd71d3" 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_019fee7a-91d6-73ab-98a9-7ea5a33bb103" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-7633-bd2c-98a3eccd71d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_PreFundedWarrantsMember_019fee7a-91d6-7639-b542-4483bd4bfb64" xlink:href="wprt-20260630.xsd#wprt_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-7633-bd2c-98a3eccd71d3" xlink:to="loc_wprt_PreFundedWarrantsMember_019fee7a-91d6-7639-b542-4483bd4bfb64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CommonWarrantsMember_019fee7a-91d6-7d08-bd08-a33aa7d8cbc9" xlink:href="wprt-20260630.xsd#wprt_CommonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019fee7a-91d6-7633-bd2c-98a3eccd71d3" xlink:to="loc_wprt_CommonWarrantsMember_019fee7a-91d6-7d08-bd08-a33aa7d8cbc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_019fa3be-0f21-7a44-b97c-e0e705df0357" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019fb85e-3c4e-773c-a462-b004cfa5f7b4" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_019fa3be-0f21-7a44-b97c-e0e705df0357" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fb85e-3c4e-7e00-a0a6-83e7c19edc72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_019fa3be-0f21-7a44-b97c-e0e705df0357" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fb85e-3c4e-7e00-a0a6-83e7c19edc72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019fb85e-3c4e-74bd-b896-f4b379d36e31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_019fa3be-0f21-7a44-b97c-e0e705df0357" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019fb85e-3c4e-74bd-b896-f4b379d36e31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019fb889-6b92-75cf-bf3f-f6c196543f27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_019fa3be-0f21-7a44-b97c-e0e705df0357" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019fb889-6b92-75cf-bf3f-f6c196543f27" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fb85e-c4ba-7623-b8e9-b256fabe531d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SharecapitalstockoptionsandotherstockbasedplansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" 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_019e8dc7-f0ed-7645-910c-46205454fcd5" 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_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8dc7-f0ed-7645-910c-46205454fcd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0" 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_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8dc7-f0ed-7645-910c-46205454fcd5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0_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_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0" xlink:to="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ed-70dd-aeda-142c2a63787e" 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_019e8dc7-f0ed-7e38-b9d9-3ab37b4386b0" xlink:to="loc_us-gaap_EquityComponentDomain_019e8dc7-f0ed-70dd-aeda-142c2a63787e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e8dc7-f0ed-7338-b52a-58788ea992a6" 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_019e8dc7-f0ed-70dd-aeda-142c2a63787e" xlink:to="loc_us-gaap_CommonStockMember_019e8dc7-f0ed-7338-b52a-58788ea992a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7199-91f4-78f72b0cfefc" 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_019e8dc7-f0ed-7645-910c-46205454fcd5" xlink:to="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7199-91f4-78f72b0cfefc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7199-91f4-78f72b0cfefc_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_019e8dc7-f0ed-7199-91f4-78f72b0cfefc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7199-91f4-78f72b0cfefc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-709f-85ca-95cfe695f3fa" 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_019e8dc7-f0ed-7199-91f4-78f72b0cfefc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-709f-85ca-95cfe695f3fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-7a0f-b1f3-09691df0c8ca" xlink:href="wprt-20260630.xsd#wprt_ShareUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-709f-85ca-95cfe695f3fa" xlink:to="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-7a0f-b1f3-09691df0c8ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8dc7-f0ed-7763-96dd-1035be40e9b0" 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_019e8dc7-f0ed-709f-85ca-95cfe695f3fa" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019e8dc7-f0ed-7763-96dd-1035be40e9b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa364-17aa-7a52-baae-87fd00963049" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019fa364-17aa-7a52-baae-87fd00963049" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019fa364-17aa-73c3-9c92-6f15ee7381b6" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_019fa364-17aa-73c3-9c92-6f15ee7381b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e8dc7-f0ed-7221-9cdc-2d04a56822b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019e8dc7-f0ed-7221-9cdc-2d04a56822b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7ad1-a651-976788a898ad" 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_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7ad1-a651-976788a898ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e8dc7-f0ed-7a3c-8ee2-c087be8d14f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e8dc7-f0ed-7a3c-8ee2-c087be8d14f3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e8dc7-f0ed-7e90-bfb6-2619be6124bc" 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_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019e8dc7-f0ed-7e90-bfb6-2619be6124bc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e8dc7-f0ed-78c6-8c21-a18da50c0a79" 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_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e8dc7-f0ed-78c6-8c21-a18da50c0a79" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e8dc7-f0ed-7e34-bec6-f246976f669b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7b18-b3b2-14aec206af8e" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e8dc7-f0ed-7e34-bec6-f246976f669b" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansShareunitsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SharecapitalstockoptionsandotherstockbasedplansShareunitsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansShareunitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" 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_019e8dc7-f0ed-7fcf-8404-9b701d985769" 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_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8dc7-f0ed-7fcf-8404-9b701d985769" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7e12-b346-a977ac51b9bc" 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_019e8dc7-f0ed-7fcf-8404-9b701d985769" xlink:to="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7e12-b346-a977ac51b9bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7e12-b346-a977ac51b9bc_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_019e8dc7-f0ed-7e12-b346-a977ac51b9bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7e12-b346-a977ac51b9bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7a46-9683-b99f31ec0bb8" 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_019e8dc7-f0ed-7e12-b346-a977ac51b9bc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7a46-9683-b99f31ec0bb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-76d5-938f-6043e07ac7c8" xlink:href="wprt-20260630.xsd#wprt_ShareUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7a46-9683-b99f31ec0bb8" xlink:to="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-76d5-938f-6043e07ac7c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" 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_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019e8dc7-f0ed-7b70-b05c-f9507935e807" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019e8dc7-f0ed-7b70-b05c-f9507935e807" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e8dc7-f0ed-719a-96a7-1ea640324b1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_019e8dc7-f0ed-719a-96a7-1ea640324b1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_019e8dc7-f0ed-768e-bc7b-c8376289becf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_019e8dc7-f0ed-768e-bc7b-c8376289becf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_019e8dc7-f0ed-7d66-b6da-5bc60bf139fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e8dc7-f0ed-710b-b394-503870e84c06" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_019e8dc7-f0ed-7d66-b6da-5bc60bf139fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_019e8dc7-f0ed-797e-ae6e-5c35434f39b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingAndExercisableNumber_019e8dc7-f0ed-780a-9ea7-70f7ac3ddfb1" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingAndExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingAndExercisableNumber_019e8dc7-f0ed-780a-9ea7-70f7ac3ddfb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_019e8dc7-f0ed-7c11-9603-03ff1043bccd" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_019e8dc7-f0ed-7c11-9603-03ff1043bccd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_019e8dc7-f0ed-712f-bc6b-e5931af35cdb" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_019e8dc7-f0ed-712f-bc6b-e5931af35cdb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue_019e8dc7-f0ed-742c-9585-7e6a5f20b797" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercisedWeightedAverageGrantDateFairValue_019e8dc7-f0ed-742c-9585-7e6a5f20b797" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue_019e8dc7-f0ed-76d9-94db-718b0a8fb36c" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_019e8dc7-f0ed-7dd4-b3b9-b1d4911e48a2" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirationsWeightedAverageGrantDateFairValue_019e8dc7-f0ed-76d9-94db-718b0a8fb36c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_019e8dc7-f0ed-74c7-a785-1e9d1d996953" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingAndExercisableWeightedAverageGrantDateFairValue_019e8dc7-f0ed-71d3-ab95-2ba02dc49bef" xlink:href="wprt-20260630.xsd#wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingAndExercisableWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-70db-9f3a-eabb0d4430ab" xlink:to="loc_wprt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingAndExercisableWeightedAverageGrantDateFairValue_019e8dc7-f0ed-71d3-ab95-2ba02dc49bef" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansAggregateintrinsicvaluesDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SharecapitalstockoptionsandotherstockbasedplansAggregateintrinsicvaluesDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansAggregateintrinsicvaluesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7661-bb4e-58228c064a1f" 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_019e8dc7-f0ed-7ba9-a0e9-8d01e74937df" 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_019e8dc7-f0ed-7661-bb4e-58228c064a1f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e8dc7-f0ed-7ba9-a0e9-8d01e74937df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7619-bbf4-965939d2b30d" 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_019e8dc7-f0ed-7ba9-a0e9-8d01e74937df" xlink:to="loc_us-gaap_AwardTypeAxis_019e8dc7-f0ed-7619-bbf4-965939d2b30d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7619-bbf4-965939d2b30d_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_019e8dc7-f0ed-7619-bbf4-965939d2b30d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7619-bbf4-965939d2b30d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7325-a0a4-87f28f33e3ec" 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_019e8dc7-f0ed-7619-bbf4-965939d2b30d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7325-a0a4-87f28f33e3ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-7c13-9a48-2cb37ff823cd" xlink:href="wprt-20260630.xsd#wprt_ShareUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e8dc7-f0ed-7325-a0a4-87f28f33e3ec" xlink:to="loc_wprt_ShareUnitsMember_019e8dc7-f0ed-7c13-9a48-2cb37ff823cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019e8dc7-f0ed-7161-9768-a53bd302c323" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7661-bb4e-58228c064a1f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_019e8dc7-f0ed-7161-9768-a53bd302c323" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019e8dc7-f0ed-7d9d-9778-17152b87131e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7661-bb4e-58228c064a1f" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_019e8dc7-f0ed-7d9d-9778-17152b87131e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019e8dc7-f0ed-7961-bcfc-d3be73c518db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e8dc7-f0ed-7661-bb4e-58228c064a1f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019e8dc7-f0ed-7961-bcfc-d3be73c518db" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8dc7-f0ed-72aa-a810-edaf0e63272f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8dc7-f0ed-72aa-a810-edaf0e63272f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e8dc7-f0ed-7805-85fa-cc5f77da9468" 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_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8dc7-f0ed-72aa-a810-edaf0e63272f" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019e8dc7-f0ed-7805-85fa-cc5f77da9468" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7b54-8941-b329d952ffe8" 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_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7b54-8941-b329d952ffe8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInShares_019e8dc7-f0ed-7886-9655-4e368f67e709" xlink:href="wprt-20260630.xsd#wprt_ShareBasedPaymentArrangementExpenseSettledInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInShares_019e8dc7-f0ed-7886-9655-4e368f67e709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInCash_019e8dc7-f0ed-7d80-b5a5-62fa1d9d5481" xlink:href="wprt-20260630.xsd#wprt_ShareBasedPaymentArrangementExpenseSettledInCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInCash_019e8dc7-f0ed-7d80-b5a5-62fa1d9d5481" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails_1" xlink:type="simple" xlink:href="wprt-20260630.xsd#SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails_1"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SharecapitalstockoptionsandotherstockbasedplansStockbasedcompensationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8dc7-f0ed-72aa-a810-edaf0e63272f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e8dc7-f0ed-72aa-a810-edaf0e63272f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7b54-8941-b329d952ffe8" 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_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e8dc7-f0ed-7b54-8941-b329d952ffe8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInShares_019e8dc7-f0ed-7886-9655-4e368f67e709" xlink:href="wprt-20260630.xsd#wprt_ShareBasedPaymentArrangementExpenseSettledInShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInShares_019e8dc7-f0ed-7886-9655-4e368f67e709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInCash_019e8dc7-f0ed-7d80-b5a5-62fa1d9d5481" xlink:href="wprt-20260630.xsd#wprt_ShareBasedPaymentArrangementExpenseSettledInCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e8dc7-f0ed-7954-b78f-375dd967fc50" xlink:to="loc_wprt_ShareBasedPaymentArrangementExpenseSettledInCash_019e8dc7-f0ed-7d80-b5a5-62fa1d9d5481" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/RelatedpartytransactionsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#RelatedpartytransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/RelatedpartytransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019e8dc7-f0ed-7027-9878-4c8333f2b22e" 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_019e8dc7-f0ed-7e0f-bdd1-d415ca0a4117" 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_019e8dc7-f0ed-7027-9878-4c8333f2b22e" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e8dc7-f0ed-7e0f-bdd1-d415ca0a4117" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ed-778c-8d1c-db0605aaa15a" 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_019e8dc7-f0ed-7e0f-bdd1-d415ca0a4117" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019e8dc7-f0ed-778c-8d1c-db0605aaa15a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ed-778c-8d1c-db0605aaa15a_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_019e8dc7-f0ed-778c-8d1c-db0605aaa15a" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ed-778c-8d1c-db0605aaa15a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ed-7317-bbe0-b2481b801c06" 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_019e8dc7-f0ed-778c-8d1c-db0605aaa15a" xlink:to="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ed-7317-bbe0-b2481b801c06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraMember_019e8dc7-f0ed-7c02-bd3b-9edf0cacc0ca" xlink:href="wprt-20260630.xsd#wprt_CespiraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019e8dc7-f0ed-7317-bbe0-b2481b801c06" xlink:to="loc_wprt_CespiraMember_019e8dc7-f0ed-7c02-bd3b-9edf0cacc0ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019e8dc7-f0ed-7212-9f5a-14c3c316ade9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019e8dc7-f0ed-7e0f-bdd1-d415ca0a4117" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019e8dc7-f0ed-7212-9f5a-14c3c316ade9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7212-9f5a-14c3c316ade9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019e8dc7-f0ed-7212-9f5a-14c3c316ade9" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7212-9f5a-14c3c316ade9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7dd1-a49a-51a8c198a3c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019e8dc7-f0ed-7212-9f5a-14c3c316ade9" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7dd1-a49a-51a8c198a3c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_SalesOfGoodsServicesAndOtherIncomeMember_019e8dc7-f0ed-74e2-8e8a-ce9a7cd44bcb" xlink:href="wprt-20260630.xsd#wprt_SalesOfGoodsServicesAndOtherIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7dd1-a49a-51a8c198a3c7" xlink:to="loc_wprt_SalesOfGoodsServicesAndOtherIncomeMember_019e8dc7-f0ed-74e2-8e8a-ce9a7cd44bcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_InventoryPurchasedServicesAndOtherExpensesMember_019e8dc7-f0ed-78d7-b445-6439b27b0440" xlink:href="wprt-20260630.xsd#wprt_InventoryPurchasedServicesAndOtherExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019e8dc7-f0ed-7dd1-a49a-51a8c198a3c7" xlink:to="loc_wprt_InventoryPurchasedServicesAndOtherExpensesMember_019e8dc7-f0ed-78d7-b445-6439b27b0440" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_019e8dc7-f0ed-7860-8db8-425e94d5a78d" 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_us-gaap_RelatedPartyTransactionLineItems_019e8dc7-f0ed-7027-9878-4c8333f2b22e" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_019e8dc7-f0ed-7860-8db8-425e94d5a78d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherReceivablesNetCurrent_019e8dc7-f0ed-7ba0-a94d-31e73c785327" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherReceivablesNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e8dc7-f0ed-7027-9878-4c8333f2b22e" xlink:to="loc_us-gaap_OtherReceivablesNetCurrent_019e8dc7-f0ed-7ba0-a94d-31e73c785327" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrentAndNoncurrent_019e8dc7-f0ed-7a2a-97f9-3b2bb58ee8b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019e8dc7-f0ed-7027-9878-4c8333f2b22e" xlink:to="loc_us-gaap_AccountsPayableCurrentAndNoncurrent_019e8dc7-f0ed-7a2a-97f9-3b2bb58ee8b0" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentinformationNarrativeDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentinformationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentinformationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-79ac-900a-bf9fe577dc44" 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_019e8dc7-f0ed-7c17-b927-09fa8c4eed3a" 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_019e8dc7-f0ed-79ac-900a-bf9fe577dc44" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7c17-b927-09fa8c4eed3a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6" 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_019e8dc7-f0ed-7c17-b927-09fa8c4eed3a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6_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_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7434-a261-356490de39c2" 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_019e8dc7-f0ed-752a-b14e-00b22fa1c1b6" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7434-a261-356490de39c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraMember_019e8dc7-f0ed-71f9-8c95-eeba54214b1d" xlink:href="wprt-20260630.xsd#wprt_CespiraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7434-a261-356490de39c2" xlink:to="loc_wprt_CespiraMember_019e8dc7-f0ed-71f9-8c95-eeba54214b1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7241-a140-013b530abaca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7c17-b927-09fa8c4eed3a" xlink:to="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7241-a140-013b530abaca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7241-a140-013b530abaca_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7241-a140-013b530abaca" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7241-a140-013b530abaca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7f0f-8c44-0ec64fc4c2d7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7241-a140-013b530abaca" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7f0f-8c44-0ec64fc4c2d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-7d62-aed3-b6dc43d86ce0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7f0f-8c44-0ec64fc4c2d7" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-7d62-aed3-b6dc43d86ce0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019e8dc7-f0ed-79ed-b181-fca4738ee331" 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_019e8dc7-f0ed-79ac-900a-bf9fe577dc44" xlink:to="loc_us-gaap_NumberOfReportableSegments_019e8dc7-f0ed-79ed-b181-fca4738ee331" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e8dc7-f0ed-7c26-91d0-d62d096c3a0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-79ac-900a-bf9fe577dc44" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e8dc7-f0ed-7c26-91d0-d62d096c3a0f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentinformationFinancialinformationbybusinesssegmentDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentinformationFinancialinformationbybusinesssegmentDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentinformationFinancialinformationbybusinesssegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" 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_019e8dc7-f0ed-7827-913f-43347eb54c65" 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_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7827-913f-43347eb54c65" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7827-913f-43347eb54c65" xlink:to="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-742d-9042-ad71c29580e0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7aa9-86f4-c5561ae5ac70" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-742d-9042-ad71c29580e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-74e4-b805-71719895feda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-742d-9042-ad71c29580e0" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-74e4-b805-71719895feda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_019e8dc7-f0ed-7df4-96b2-ab29335d59aa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-742d-9042-ad71c29580e0" xlink:to="loc_srt_ConsolidationEliminationsMember_019e8dc7-f0ed-7df4-96b2-ab29335d59aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-7dc8-a41b-40ac590802c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-742d-9042-ad71c29580e0" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-7dc8-a41b-40ac590802c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-730a-bb2d-526186bff2c2" 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_019e8dc7-f0ed-7827-913f-43347eb54c65" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-730a-bb2d-526186bff2c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-730a-bb2d-526186bff2c2_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_019e8dc7-f0ed-730a-bb2d-526186bff2c2" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-730a-bb2d-526186bff2c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7cb2-a596-5bdb7ba79da6" 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_019e8dc7-f0ed-730a-bb2d-526186bff2c2" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7cb2-a596-5bdb7ba79da6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HighPressureControlsMember_019e8dc7-f0ed-7e39-aaa4-ff676b446edf" xlink:href="wprt-20260630.xsd#wprt_HighPressureControlsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7cb2-a596-5bdb7ba79da6" xlink:to="loc_wprt_HighPressureControlsMember_019e8dc7-f0ed-7e39-aaa4-ff676b446edf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HeavyDutyOEMMember_019e8dc7-f0ed-71e5-85cc-59519251f4d0" xlink:href="wprt-20260630.xsd#wprt_HeavyDutyOEMMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7cb2-a596-5bdb7ba79da6" xlink:to="loc_wprt_HeavyDutyOEMMember_019e8dc7-f0ed-71e5-85cc-59519251f4d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8dc7-f0ed-7b36-ae98-b27c79189781" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e8dc7-f0ed-7b36-ae98-b27c79189781" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019e8dc7-f0ed-794f-8ad8-2c50a6ccced7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019e8dc7-f0ed-794f-8ad8-2c50a6ccced7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019e8dc7-f0ed-7487-a603-057117a892e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_GrossProfit_019e8dc7-f0ed-7487-a603-057117a892e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019e8dc7-f0ed-7996-93ca-d77d1e29a37d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019e8dc7-f0ed-7996-93ca-d77d1e29a37d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019e8dc7-f0ed-78fa-9aaf-8ab4b169ba56" 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_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019e8dc7-f0ed-78fa-9aaf-8ab4b169ba56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_019e8dc7-f0ed-7c14-bd9d-aa1985af1ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_SellingAndMarketingExpense_019e8dc7-f0ed-7c14-bd9d-aa1985af1ad4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAmortizationAndAccretionNet_019e8dc7-f0ed-7f71-a71b-8c207ae0a3a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_DepreciationAmortizationAndAccretionNet_019e8dc7-f0ed-7f71-a71b-8c207ae0a3a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_OperatingExpensesIncludingDepreciationAmortizationAndAccretionNet_019e8dc7-f0ed-7827-9b4a-afd6a19525ea" xlink:href="wprt-20260630.xsd#wprt_OperatingExpensesIncludingDepreciationAmortizationAndAccretionNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_wprt_OperatingExpensesIncludingDepreciationAmortizationAndAccretionNet_019e8dc7-f0ed-7827-9b4a-afd6a19525ea" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019e8dc7-f0ed-718b-a993-368c8dd847be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019e8dc7-f0ed-718b-a993-368c8dd847be" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization_019e8dc7-f0ed-7a47-8e62-a22055ec4756" xlink:href="wprt-20260630.xsd#wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization_019e8dc7-f0ed-7a47-8e62-a22055ec4756" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019e8dc7-f0ed-7395-a20f-d0e7f9e79343" 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_SegmentReportingInformationLineItems_019e8dc7-f0ed-75b1-ac0b-6d7777f020f5" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019e8dc7-f0ed-7395-a20f-d0e7f9e79343" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentInformationReconciliationofSegmentEBITDAtoLossbeforeincometaxesDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentInformationReconciliationofSegmentEBITDAtoLossbeforeincometaxesDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentInformationReconciliationofSegmentEBITDAtoLossbeforeincometaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" 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_019e8dc7-f0ed-7121-9d71-85a0ac84c9ab" 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_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7121-9d71-85a0ac84c9ab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7e1c-937b-501df41c6f8c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7121-9d71-85a0ac84c9ab" xlink:to="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7e1c-937b-501df41c6f8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7e1c-937b-501df41c6f8c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7e1c-937b-501df41c6f8c" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7e1c-937b-501df41c6f8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7291-9e15-53df360a3449" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7e1c-937b-501df41c6f8c" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7291-9e15-53df360a3449" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-746c-adf3-55738dc1b994" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7291-9e15-53df360a3449" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-746c-adf3-55738dc1b994" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-7e77-870d-eb7cc30cece8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7291-9e15-53df360a3449" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-7e77-870d-eb7cc30cece8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-7f7b-8580-1776fbdd155f" 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_019e8dc7-f0ed-7121-9d71-85a0ac84c9ab" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-7f7b-8580-1776fbdd155f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7f7b-8580-1776fbdd155f_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_019e8dc7-f0ed-7f7b-8580-1776fbdd155f" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7f7b-8580-1776fbdd155f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7ba9-820b-7c72d6da4915" 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_019e8dc7-f0ed-7f7b-8580-1776fbdd155f" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7ba9-820b-7c72d6da4915" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_CespiraMember_019e8dc7-f0ed-7580-9ae4-452cc29cf093" xlink:href="wprt-20260630.xsd#wprt_CespiraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7ba9-820b-7c72d6da4915" xlink:to="loc_wprt_CespiraMember_019e8dc7-f0ed-7580-9ae4-452cc29cf093" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization_019e8dc7-f0ed-7038-949c-209df5ca70e8" xlink:href="wprt-20260630.xsd#wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_wprt_SegmentEarningsBeforeInterestTaxDepreciationAndAmortization_019e8dc7-f0ed-7038-949c-209df5ca70e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019e8dc7-f0ed-7b5a-8ab3-d475d191949c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019e8dc7-f0ed-7b5a-8ab3-d475d191949c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019e8dc7-f0ed-753a-90d1-ff1ac038f34f" 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_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019e8dc7-f0ed-753a-90d1-ff1ac038f34f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019e8dc7-f0ed-7de2-9787-ac38aa2a8dde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_OperatingExpenses_019e8dc7-f0ed-7de2-9787-ac38aa2a8dde" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019e8dc7-f0ed-7306-b7ea-7cc129be9753" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_019e8dc7-f0ed-7306-b7ea-7cc129be9753" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAdjustmentOfWarrants_019fa369-39b9-7082-be14-d191a96f3366" 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_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_FairValueAdjustmentOfWarrants_019fa369-39b9-7082-be14-d191a96f3366" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_FinancingTransactionCosts_019fb880-6d68-76c2-9d78-200ff79f7e7a" xlink:href="wprt-20260630.xsd#wprt_FinancingTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_wprt_FinancingTransactionCosts_019fb880-6d68-76c2-9d78-200ff79f7e7a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019e8dc7-f0ed-7377-b0b2-b644a915daf1" 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_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_InterestExpenseDebt_019e8dc7-f0ed-7377-b0b2-b644a915daf1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ed-79a6-a1cf-320d03441b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_019e8dc7-f0ed-79a6-a1cf-320d03441b7c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8dc7-f0ed-7f4d-890b-efad406b3f95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-7036-b586-4cd68c198e9e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e8dc7-f0ed-7f4d-890b-efad406b3f95" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentinformationAssetsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentinformationAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentinformationAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-73bd-9adf-6dc20d999763" 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_019e8dc7-f0ed-7661-b356-6f09a23d44db" 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_019e8dc7-f0ed-73bd-9adf-6dc20d999763" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7661-b356-6f09a23d44db" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7661-b356-6f09a23d44db" xlink:to="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-74de-94bd-a8a2520d99a3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f0ed-7a10-a9f2-2cfff5318e41" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-74de-94bd-a8a2520d99a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-77b0-b228-10b16e387fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-74de-94bd-a8a2520d99a3" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f0ed-77b0-b228-10b16e387fbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-799c-af80-0ea51f884124" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f0ed-74de-94bd-a8a2520d99a3" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f0ed-799c-af80-0ea51f884124" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-7178-ab29-35d025d30d61" 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_019e8dc7-f0ed-7661-b356-6f09a23d44db" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f0ed-7178-ab29-35d025d30d61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7178-ab29-35d025d30d61_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_019e8dc7-f0ed-7178-ab29-35d025d30d61" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-7178-ab29-35d025d30d61_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-75cf-8611-8f210f0012f5" 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_019e8dc7-f0ed-7178-ab29-35d025d30d61" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-75cf-8611-8f210f0012f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HighPressureControlsMember_019e8dc7-f0ed-7e71-ad61-05adee41ecde" xlink:href="wprt-20260630.xsd#wprt_HighPressureControlsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f0ed-75cf-8611-8f210f0012f5" xlink:to="loc_wprt_HighPressureControlsMember_019e8dc7-f0ed-7e71-ad61-05adee41ecde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e8dc7-f0ed-75cd-bf63-1884bb72bef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f0ed-73bd-9adf-6dc20d999763" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019e8dc7-f0ed-75cd-bf63-1884bb72bef2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentinformationPercentofrevenuebygeographicallocationDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentinformationPercentofrevenuebygeographicallocationDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentinformationPercentofrevenuebygeographicallocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f1ab-7b61-9cec-81175ca719f5" 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_019e8dc7-f0ed-7c0b-b6f2-1108d3603c9b" 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_019e8dc7-f1ab-7b61-9cec-81175ca719f5" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7c0b-b6f2-1108d3603c9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e8dc7-f0ed-7303-9503-95cc8305bf3c" 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_019e8dc7-f0ed-7c0b-b6f2-1108d3603c9b" xlink:to="loc_srt_StatementGeographicalAxis_019e8dc7-f0ed-7303-9503-95cc8305bf3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-7303-9503-95cc8305bf3c_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_019e8dc7-f0ed-7303-9503-95cc8305bf3c" xlink:to="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-7303-9503-95cc8305bf3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-755d-a770-b4239ee9698e" 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_019e8dc7-f0ed-7303-9503-95cc8305bf3c" xlink:to="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-755d-a770-b4239ee9698e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaMember_019e8dc7-f0ed-718f-9285-d0a0ae8baec9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AsiaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-755d-a770-b4239ee9698e" xlink:to="loc_srt_AsiaMember_019e8dc7-f0ed-718f-9285-d0a0ae8baec9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AmericasMember_019e8dc7-f0ed-786a-8b9f-80e5e21cca2c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_AmericasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-755d-a770-b4239ee9698e" xlink:to="loc_srt_AmericasMember_019e8dc7-f0ed-786a-8b9f-80e5e21cca2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_019e8dc7-f0ed-7cd4-b336-c662c0447255" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e8dc7-f0ed-755d-a770-b4239ee9698e" xlink:to="loc_srt_EuropeMember_019e8dc7-f0ed-7cd4-b336-c662c0447255" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8dc7-f0ed-7037-89ed-ec05f1c70008" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7c0b-b6f2-1108d3603c9b" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8dc7-f0ed-7037-89ed-ec05f1c70008" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8dc7-f0ed-7037-89ed-ec05f1c70008_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8dc7-f0ed-7037-89ed-ec05f1c70008" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8dc7-f0ed-7037-89ed-ec05f1c70008_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e8dc7-f1ab-756b-ac7f-7dea3c019b28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e8dc7-f0ed-7037-89ed-ec05f1c70008" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e8dc7-f1ab-756b-ac7f-7dea3c019b28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019e8dc7-f1ab-7961-9bbf-a34ca08098ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e8dc7-f1ab-756b-ac7f-7dea3c019b28" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019e8dc7-f1ab-7961-9bbf-a34ca08098ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8dc7-f1ab-7be6-9a05-bb421397d433" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f0ed-7c0b-b6f2-1108d3603c9b" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8dc7-f1ab-7be6-9a05-bb421397d433" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8dc7-f1ab-7be6-9a05-bb421397d433_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8dc7-f1ab-7be6-9a05-bb421397d433" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8dc7-f1ab-7be6-9a05-bb421397d433_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8dc7-f1ab-7b82-8ade-ad8c1b1a9ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e8dc7-f1ab-7be6-9a05-bb421397d433" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8dc7-f1ab-7b82-8ade-ad8c1b1a9ea7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueProductLineMember_019e8dc7-f1ab-7435-af49-229765ae37f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueProductLineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e8dc7-f1ab-7b82-8ade-ad8c1b1a9ea7" xlink:to="loc_us-gaap_SalesRevenueProductLineMember_019e8dc7-f1ab-7435-af49-229765ae37f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e8dc7-f1ab-734f-a7f9-6c857d29016d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f1ab-7b61-9cec-81175ca719f5" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e8dc7-f1ab-734f-a7f9-6c857d29016d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/SegmentInformationTotalassetallocationDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#SegmentInformationTotalassetallocationDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/SegmentInformationTotalassetallocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f1ab-738a-8209-c4e26c3fb3d9" 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_019e8dc7-f1ab-7f83-a50e-0ef60c3b5d92" 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_019e8dc7-f1ab-738a-8209-c4e26c3fb3d9" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f1ab-7f83-a50e-0ef60c3b5d92" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019e8dc7-f1ab-7f83-a50e-0ef60c3b5d92" xlink:to="loc_srt_ConsolidationItemsAxis_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-7f07-ab97-4fb7f155001b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019e8dc7-f1ab-70c3-bb96-7a6cf3b1384e" xlink:to="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-7f07-ab97-4fb7f155001b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f1ab-7574-b85d-4f9d01afb8af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-7f07-ab97-4fb7f155001b" xlink:to="loc_us-gaap_OperatingSegmentsMember_019e8dc7-f1ab-7574-b85d-4f9d01afb8af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f1ab-7eeb-88a9-5756e26e6563" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019e8dc7-f1ab-7f07-ab97-4fb7f155001b" xlink:to="loc_us-gaap_CorporateNonSegmentMember_019e8dc7-f1ab-7eeb-88a9-5756e26e6563" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f1ab-71df-abc9-33a231c20ad8" 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_019e8dc7-f1ab-7f83-a50e-0ef60c3b5d92" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019e8dc7-f1ab-71df-abc9-33a231c20ad8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f1ab-71df-abc9-33a231c20ad8_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_019e8dc7-f1ab-71df-abc9-33a231c20ad8" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f1ab-71df-abc9-33a231c20ad8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019e8dc7-f1ab-7c27-b185-db70e98984e1" 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_019e8dc7-f1ab-71df-abc9-33a231c20ad8" xlink:to="loc_us-gaap_SegmentDomain_019e8dc7-f1ab-7c27-b185-db70e98984e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_HighPressureControlsMember_019e8dc7-f1ab-70e3-98df-d4281c3d2016" xlink:href="wprt-20260630.xsd#wprt_HighPressureControlsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019e8dc7-f1ab-7c27-b185-db70e98984e1" xlink:to="loc_wprt_HighPressureControlsMember_019e8dc7-f1ab-70e3-98df-d4281c3d2016" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019e8dc7-f1ab-734b-886a-3a9344255809" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019e8dc7-f1ab-738a-8209-c4e26c3fb3d9" xlink:to="loc_us-gaap_Assets_019e8dc7-f1ab-734b-886a-3a9344255809" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.westport.com/role/FinancialinstrumentsFinancialObligationsDetails" xlink:type="simple" xlink:href="wprt-20260630.xsd#FinancialinstrumentsFinancialObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.westport.com/role/FinancialinstrumentsFinancialObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" 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_019e8dc7-f1ab-7493-b8ca-08f46c39170f" 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_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_us-gaap_OtherCommitmentsTable_019e8dc7-f1ab-7493-b8ca-08f46c39170f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ContractualObligationsTypeAxis_019e8dc7-f1ab-734a-b6ef-e870147475e9" xlink:href="wprt-20260630.xsd#wprt_ContractualObligationsTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019e8dc7-f1ab-7493-b8ca-08f46c39170f" xlink:to="loc_wprt_ContractualObligationsTypeAxis_019e8dc7-f1ab-734a-b6ef-e870147475e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-734a-b6ef-e870147475e9_default" xlink:href="wprt-20260630.xsd#wprt_ContractualObligationsTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_wprt_ContractualObligationsTypeAxis_019e8dc7-f1ab-734a-b6ef-e870147475e9" xlink:to="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-734a-b6ef-e870147475e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-7482-8a73-11c9085b21ff" xlink:href="wprt-20260630.xsd#wprt_ContractualObligationsTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_wprt_ContractualObligationsTypeAxis_019e8dc7-f1ab-734a-b6ef-e870147475e9" xlink:to="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-7482-8a73-11c9085b21ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_AccountsPayableAndAccruedLiabilitiesCurrentMember_019e8dc7-f1ab-749d-b9d1-c1378e8570cd" xlink:href="wprt-20260630.xsd#wprt_AccountsPayableAndAccruedLiabilitiesCurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-7482-8a73-11c9085b21ff" xlink:to="loc_wprt_AccountsPayableAndAccruedLiabilitiesCurrentMember_019e8dc7-f1ab-749d-b9d1-c1378e8570cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019e8dc7-f1ab-7e6d-bfa3-5f036eb3be86" 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_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-7482-8a73-11c9085b21ff" xlink:to="loc_us-gaap_SecuredDebtMember_019e8dc7-f1ab-7e6d-bfa3-5f036eb3be86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_OperatingLeaseExpensesMember_019e8dc7-f1ab-76b0-a151-62de0271c745" xlink:href="wprt-20260630.xsd#wprt_OperatingLeaseExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_wprt_ContractualObligationsTypeDomain_019e8dc7-f1ab-7482-8a73-11c9085b21ff" xlink:to="loc_wprt_OperatingLeaseExpensesMember_019e8dc7-f1ab-76b0-a151-62de0271c745" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligation_019e8dc7-f1ab-75ca-918c-d4d990f84ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_us-gaap_ContractualObligation_019e8dc7-f1ab-75ca-918c-d4d990f84ce6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_wprt_ContractualObligationsRepaymentsTotal_019e8dc7-f1ab-7997-9f0b-ee294704fc2e" xlink:href="wprt-20260630.xsd#wprt_ContractualObligationsRepaymentsTotal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_wprt_ContractualObligationsRepaymentsTotal_019e8dc7-f1ab-7997-9f0b-ee294704fc2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInNextTwelveMonths_019e8dc7-f1ab-7197-a203-a4d67f450082" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_us-gaap_ContractualObligationDueInNextTwelveMonths_019e8dc7-f1ab-7197-a203-a4d67f450082" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInSecondAndThirdYear_019e8dc7-f1ab-70a8-b061-49eb5f51bb67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligationDueInSecondAndThirdYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_us-gaap_ContractualObligationDueInSecondAndThirdYear_019e8dc7-f1ab-70a8-b061-49eb5f51bb67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInFourthAndFifthYear_019e8dc7-f1ab-7771-b593-20e1aebdcd51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractualObligationDueInFourthAndFifthYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019e8dc7-f1ab-7731-8b36-41fef91a5bf8" xlink:to="loc_us-gaap_ContractualObligationDueInFourthAndFifthYear_019e8dc7-f1ab-7771-b593-20e1aebdcd51" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
