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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a083a5-0130-71c2-b630-d4a47268d9d5,g:a53b0904-8419-446d-85de-da31013a4740-->
<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.graftech.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="gti-20260930.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a083a5-01ce-752b-80e4-97d9e5242995" 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_01a083a5-01ce-783a-a930-74444b36f496" 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_01a083a5-01ce-752b-80e4-97d9e5242995" xlink:to="loc_us-gaap_StatementTable_01a083a5-01ce-783a-a930-74444b36f496" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6" 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_01a083a5-01ce-783a-a930-74444b36f496" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6_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_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6" xlink:to="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-7da8-83ee-75930b175c61" 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_01a083a5-01ce-7ee5-af20-56b6ac0f7ad6" xlink:to="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-7da8-83ee-75930b175c61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a083a5-01ce-7a10-8454-689213259003" 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_01a083a5-01ce-7da8-83ee-75930b175c61" xlink:to="loc_us-gaap_CommonStockMember_01a083a5-01ce-7a10-8454-689213259003" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a083a5-01ce-79a6-9a32-ea6443227b1b" 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_01a083a5-01ce-7da8-83ee-75930b175c61" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a083a5-01ce-79a6-9a32-ea6443227b1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a083a5-01ce-77b2-96cc-6421201fd367" 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_01a083a5-01ce-7da8-83ee-75930b175c61" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a083a5-01ce-77b2-96cc-6421201fd367" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a083a5-01ce-70e5-b6d1-aa952bbb5775" 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_01a083a5-01ce-7da8-83ee-75930b175c61" xlink:to="loc_us-gaap_RetainedEarningsMember_01a083a5-01ce-70e5-b6d1-aa952bbb5775" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" 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_01a083a5-01ce-752b-80e4-97d9e5242995" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_01a083a5-01ce-7c95-94a2-91d26752bc09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_SharesIssued_01a083a5-01ce-7c95-94a2-91d26752bc09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a083a5-01ce-7b21-a0d9-ec2d3fb6f49e" 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_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_StockholdersEquity_01a083a5-01ce-7b21-a0d9-ec2d3fb6f49e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7cf1-b437-271afd3ef71f" 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_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7cf1-b437-271afd3ef71f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a083a5-01ce-73c4-a7d6-0f9115d45edf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_01a083a5-01ce-73c4-a7d6-0f9115d45edf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a083a5-01ce-7d82-8a16-364e50b55c58" 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_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01a083a5-01ce-7d82-8a16-364e50b55c58" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a083a5-01ce-78e2-abd6-48401c96e340" 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_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a083a5-01ce-78e2-abd6-48401c96e340" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_01a083a5-01ce-7c94-aefe-6956b3c412b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_01a083a5-01ce-7c94-aefe-6956b3c412b5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_01a083a5-01ce-73ef-a3a5-e5b9ef6136d6" 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_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_01a083a5-01ce-73ef-a3a5-e5b9ef6136d6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock_01a083a5-01ce-79c0-a686-7e4372d30979" xlink:href="gti-20260930.xsd#gti_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_gti_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock_01a083a5-01ce-79c0-a686-7e4372d30979" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_01a083a5-01ce-7d2e-ad79-232f6c272e28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_01a083a5-01ce-7d2e-ad79-232f6c272e28" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_01a083a5-01ce-7dd9-bef5-af3419b6a8f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7411-b6a8-060cb8c640ca" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_01a083a5-01ce-7dd9-bef5-af3419b6a8f7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_01a083a5-01ce-7238-bfb6-7e325b23d0c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a083a5-01ce-7f87-ba4b-785233b0eaa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/RevenuefromContractswithCustomersDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#RevenuefromContractswithCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/RevenuefromContractswithCustomersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01a083a5-01ce-76f2-a6c8-0debe20a0d36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_01a083a5-01ce-7d08-a335-a75778b436bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01a083a5-01ce-76f2-a6c8-0debe20a0d36" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a083a5-01ce-7d08-a335-a75778b436bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb" 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_DisaggregationOfRevenueTable_01a083a5-01ce-7d08-a335-a75778b436bf" xlink:to="loc_srt_ProductOrServiceAxis_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb_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_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb" xlink:to="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7708-95bd-6e79ca71d6fc" 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_01a083a5-01ce-7c08-bf3d-5c4b4d6590cb" xlink:to="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7708-95bd-6e79ca71d6fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_GraphiteElectrodesMember_01a083a5-01ce-7b99-b457-4cbaf62110e2" xlink:href="gti-20260930.xsd#gti_GraphiteElectrodesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7708-95bd-6e79ca71d6fc" xlink:to="loc_gti_GraphiteElectrodesMember_01a083a5-01ce-7b99-b457-4cbaf62110e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_ByProductsAndOtherMember_01a083a5-01ce-7491-8513-ba8a7363e64a" xlink:href="gti-20260930.xsd#gti_ByProductsAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-7708-95bd-6e79ca71d6fc" xlink:to="loc_gti_ByProductsAndOtherMember_01a083a5-01ce-7491-8513-ba8a7363e64a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a083a5-01ce-7b51-8e61-1175c7917bf3" 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_DisaggregationOfRevenueLineItems_01a083a5-01ce-76f2-a6c8-0debe20a0d36" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a083a5-01ce-7b51-8e61-1175c7917bf3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/SegmentReportingScheduleofOperatingSegmentsDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#SegmentReportingScheduleofOperatingSegmentsDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/SegmentReportingScheduleofOperatingSegmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" 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_01a083a5-01ce-7b7c-a5b7-6012b86dedf2" 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_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a083a5-01ce-7b7c-a5b7-6012b86dedf2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a083a5-01ce-77f7-998f-46d42812d932" 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_01a083a5-01ce-7b7c-a5b7-6012b86dedf2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a083a5-01ce-77f7-998f-46d42812d932" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a083a5-01ce-77f7-998f-46d42812d932_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_01a083a5-01ce-77f7-998f-46d42812d932" xlink:to="loc_us-gaap_SegmentDomain_01a083a5-01ce-77f7-998f-46d42812d932_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a083a5-01ce-71f1-85e3-85427a726939" 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_01a083a5-01ce-77f7-998f-46d42812d932" xlink:to="loc_us-gaap_SegmentDomain_01a083a5-01ce-71f1-85e3-85427a726939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_IndustrialMaterialsSegmentMember_01a083a5-01ce-7829-9131-df4e04bb5f64" xlink:href="gti-20260930.xsd#gti_IndustrialMaterialsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a083a5-01ce-71f1-85e3-85427a726939" xlink:to="loc_gti_IndustrialMaterialsSegmentMember_01a083a5-01ce-7829-9131-df4e04bb5f64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a083a5-01ce-7b4f-b5b7-5a29f5abdaa2" 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_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a083a5-01ce-7b4f-b5b7-5a29f5abdaa2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_CashCostOfGoodsSold_01a083a5-01ce-725d-9308-820f0f1ec1e4" xlink:href="gti-20260930.xsd#gti_CashCostOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_gti_CashCostOfGoodsSold_01a083a5-01ce-725d-9308-820f0f1ec1e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_01a083a5-01ce-7d87-bf9d-4ba85ae03cb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_01a083a5-01ce-7d87-bf9d-4ba85ae03cb1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWriteDown_01a083a5-01ce-7a07-9873-65d41660161e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryWriteDown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_InventoryWriteDown_01a083a5-01ce-7a07-9873-65d41660161e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a083a5-01ce-71d5-9e96-16107228bb0e" 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_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a083a5-01ce-71d5-9e96-16107228bb0e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a083a5-01ce-77c0-8e03-dada109812ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a083a5-01ce-77c0-8e03-dada109812ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_01a14072-c976-70e2-a87b-cb6de480eba1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_RestructuringCharges_01a14072-c976-70e2-a87b-cb6de480eba1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_01a083a5-01ce-7743-b4f0-0dfd1499d928" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_01a083a5-01ce-7743-b4f0-0dfd1499d928" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_01a083a5-01ce-7234-a6b6-1f0ada8c98bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_InterestExpense_01a083a5-01ce-7234-a6b6-1f0ada8c98bd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOther_01a083a5-01ce-7428-919f-f3d93d73cd8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_InterestIncomeOther_01a083a5-01ce-7428-919f-f3d93d73cd8b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a083a5-01ce-7c2e-bb4b-79e0656f9b52" 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_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a083a5-01ce-7c2e-bb4b-79e0656f9b52" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7d3e-bc5f-6a158c804890" 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_SegmentReportingInformationLineItems_01a083a5-01ce-7d6d-97c5-f8677484aace" xlink:to="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7d3e-bc5f-6a158c804890" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/SegmentReportingNarrativeDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#SegmentReportingNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/SegmentReportingNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_01a083a5-01ce-7bd7-a9a2-00bae74e8fac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_01a083a5-01ce-7bd7-a9a2-00bae74e8fac" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a083a5-01ce-76d8-b572-19da898e3283" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:to="loc_srt_MajorCustomersAxis_01a083a5-01ce-76d8-b572-19da898e3283" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a083a5-01ce-76d8-b572-19da898e3283_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a083a5-01ce-76d8-b572-19da898e3283" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a083a5-01ce-76d8-b572-19da898e3283_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a083a5-01ce-715c-b3a6-913549a231ac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a083a5-01ce-76d8-b572-19da898e3283" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a083a5-01ce-715c-b3a6-913549a231ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_ExternalCustomersMember_01a083a5-01ce-7e2f-a960-a5489fee16c9" xlink:href="gti-20260930.xsd#gti_ExternalCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a083a5-01ce-715c-b3a6-913549a231ac" xlink:to="loc_gti_ExternalCustomersMember_01a083a5-01ce-7e2f-a960-a5489fee16c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a083a5-01ce-711b-8422-0661a4221c6a" 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_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:to="loc_srt_ProductOrServiceAxis_01a083a5-01ce-711b-8422-0661a4221c6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-711b-8422-0661a4221c6a_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_01a083a5-01ce-711b-8422-0661a4221c6a" xlink:to="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-711b-8422-0661a4221c6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-726b-9de9-a2c5a574cc64" 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_01a083a5-01ce-711b-8422-0661a4221c6a" xlink:to="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-726b-9de9-a2c5a574cc64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_GraphiteElectrodesMember_01a083a5-01ce-774d-805a-33c2a6afce5d" xlink:href="gti-20260930.xsd#gti_GraphiteElectrodesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a083a5-01ce-726b-9de9-a2c5a574cc64" xlink:to="loc_gti_GraphiteElectrodesMember_01a083a5-01ce-774d-805a-33c2a6afce5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a083a5-01ce-7368-a7ef-cc83834f952b" 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_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a083a5-01ce-7368-a7ef-cc83834f952b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a083a5-01ce-7368-a7ef-cc83834f952b_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_01a083a5-01ce-7368-a7ef-cc83834f952b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a083a5-01ce-7368-a7ef-cc83834f952b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a083a5-01ce-77b8-8823-f0c498394fc4" 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_01a083a5-01ce-7368-a7ef-cc83834f952b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a083a5-01ce-77b8-8823-f0c498394fc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_01a083a5-01ce-7553-b325-83ea8797c257" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a083a5-01ce-77b8-8823-f0c498394fc4" xlink:to="loc_us-gaap_SalesRevenueNetMember_01a083a5-01ce-7553-b325-83ea8797c257" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a083a5-01ce-72b2-9fde-193d4e05f71e" 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_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_01a083a5-01ce-7bcd-9f35-503658866d34" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a083a5-01ce-72b2-9fde-193d4e05f71e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a083a5-01ce-72b2-9fde-193d4e05f71e_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_01a083a5-01ce-72b2-9fde-193d4e05f71e" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a083a5-01ce-72b2-9fde-193d4e05f71e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a083a5-01ce-775b-9c52-9fc95256ef5a" 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_01a083a5-01ce-72b2-9fde-193d4e05f71e" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a083a5-01ce-775b-9c52-9fc95256ef5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a083a5-01ce-7969-9297-f9b0fe7de109" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a083a5-01ce-775b-9c52-9fc95256ef5a" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a083a5-01ce-7969-9297-f9b0fe7de109" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_01a083a5-01ce-7ab1-9fa4-da2ca104de5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_01a083a5-01ce-7bd7-a9a2-00bae74e8fac" xlink:to="loc_us-gaap_NumberOfOperatingSegments_01a083a5-01ce-7ab1-9fa4-da2ca104de5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_01a083a5-01ce-7ff4-a036-e726c067c8c5" 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_EntityWideInformationRevenueFromExternalCustomerLineItems_01a083a5-01ce-7bd7-a9a2-00bae74e8fac" xlink:to="loc_us-gaap_NumberOfReportableSegments_01a083a5-01ce-7ff4-a036-e726c067c8c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a083a5-01ce-74f3-a65c-af9603d466c9" 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_EntityWideInformationRevenueFromExternalCustomerLineItems_01a083a5-01ce-7bd7-a9a2-00bae74e8fac" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a083a5-01ce-74f3-a65c-af9603d466c9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/IntangibleAssetsScheduleofIntangibleAssetswithDeterminableUsefulLivesbyMajorCategoryDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#IntangibleAssetsScheduleofIntangibleAssetswithDeterminableUsefulLivesbyMajorCategoryDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/IntangibleAssetsScheduleofIntangibleAssetswithDeterminableUsefulLivesbyMajorCategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a083a5-01ce-7a67-8df9-fd8a19e18cad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a083a5-01ce-74ed-a80c-647a7d8616a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a083a5-01ce-7a67-8df9-fd8a19e18cad" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a083a5-01ce-74ed-a80c-647a7d8616a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a083a5-01ce-7c67-8368-cf11287af2d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a083a5-01ce-74ed-a80c-647a7d8616a8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a083a5-01ce-7c67-8368-cf11287af2d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7c67-8368-cf11287af2d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a083a5-01ce-7c67-8368-cf11287af2d2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7c67-8368-cf11287af2d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7049-be96-dd0b6d94b4d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a083a5-01ce-7c67-8368-cf11287af2d2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7049-be96-dd0b6d94b4d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_01a083a5-01ce-7c95-83d3-0e6298ea5b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7049-be96-dd0b6d94b4d9" xlink:to="loc_us-gaap_TradeNamesMember_01a083a5-01ce-7c95-83d3-0e6298ea5b1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a083a5-01ce-7e61-a17b-35cc9d28a3e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7049-be96-dd0b6d94b4d9" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a083a5-01ce-7e61-a17b-35cc9d28a3e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_01a083a5-01ce-70a3-9c85-ef58a379770f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelatedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a083a5-01ce-7049-be96-dd0b6d94b4d9" xlink:to="loc_us-gaap_CustomerRelatedIntangibleAssetsMember_01a083a5-01ce-70a3-9c85-ef58a379770f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a083a5-01ce-7136-8198-a2ad678037d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a083a5-01ce-7a67-8df9-fd8a19e18cad" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a083a5-01ce-7136-8198-a2ad678037d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a083a5-01ce-7439-8df9-c1cc97b1385a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a083a5-01ce-7a67-8df9-fd8a19e18cad" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a083a5-01ce-7439-8df9-c1cc97b1385a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a083a5-01ce-7c05-bfa1-e903d3f1634a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a083a5-01ce-7a67-8df9-fd8a19e18cad" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a083a5-01ce-7c05-bfa1-e903d3f1634a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/DebtandLiquiditySummaryofLongTermDebtDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#DebtandLiquiditySummaryofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/DebtandLiquiditySummaryofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7c01-ba32-02b5f8a62a31" 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_01a083a5-01ce-78e2-8394-12c9c4d4fe7c" 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_01a083a5-01ce-7c01-ba32-02b5f8a62a31" xlink:to="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-78e2-8394-12c9c4d4fe7c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-7ab5-8e11-be8ae4fb0255" 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_01a083a5-01ce-78e2-8394-12c9c4d4fe7c" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-7ab5-8e11-be8ae4fb0255" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7ab5-8e11-be8ae4fb0255_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_01a083a5-01ce-7ab5-8e11-be8ae4fb0255" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7ab5-8e11-be8ae4fb0255_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" 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_01a083a5-01ce-7ab5-8e11-be8ae4fb0255" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_InitialFirstLienTermLoansMember_01a083a5-01ce-7e4c-bf2a-f1823e4816d7" xlink:href="gti-20260930.xsd#gti_InitialFirstLienTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_gti_InitialFirstLienTermLoansMember_01a083a5-01ce-7e4c-bf2a-f1823e4816d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-77b0-ac93-2fccd6129201" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-77b0-ac93-2fccd6129201" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_Existing4.625SeniorNotesMember_01a083a5-01ce-704e-b531-fc5b7cfc9bd3" xlink:href="gti-20260930.xsd#gti_Existing4.625SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_gti_Existing4.625SeniorNotesMember_01a083a5-01ce-704e-b531-fc5b7cfc9bd3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_New4.625SecondLienNotesMember_01a083a5-01ce-7b22-be68-818a132d81df" xlink:href="gti-20260930.xsd#gti_New4.625SecondLienNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_gti_New4.625SecondLienNotesMember_01a083a5-01ce-7b22-be68-818a132d81df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_Existing9.875SeniorNotesMember_01a083a5-01ce-76ae-9ea5-8701ae055676" xlink:href="gti-20260930.xsd#gti_Existing9.875SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_gti_Existing9.875SeniorNotesMember_01a083a5-01ce-76ae-9ea5-8701ae055676" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_New9.875SecondLienNotesMember_01a083a5-01ce-7f34-b3d0-87994934b9b8" xlink:href="gti-20260930.xsd#gti_New9.875SecondLienNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7adc-a13b-677f7834aa9f" xlink:to="loc_gti_New9.875SecondLienNotesMember_01a083a5-01ce-7f34-b3d0-87994934b9b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a083a5-01ce-74cd-972e-b7ade94b8950" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7c01-ba32-02b5f8a62a31" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a083a5-01ce-74cd-972e-b7ade94b8950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a083a5-01ce-7ac2-b74e-33fc351ca583" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7c01-ba32-02b5f8a62a31" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a083a5-01ce-7ac2-b74e-33fc351ca583" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_01a083a5-01ce-7ed5-a9dc-31ea893f3dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7c01-ba32-02b5f8a62a31" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_01a083a5-01ce-7ed5-a9dc-31ea893f3dd5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_01a083a5-01ce-7410-9d71-c4bf04b7121e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7c01-ba32-02b5f8a62a31" xlink:to="loc_us-gaap_LongTermDebt_01a083a5-01ce-7410-9d71-c4bf04b7121e" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/DebtandLiquidityNarrativeDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#DebtandLiquidityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/DebtandLiquidityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7323-8425-ff6b1f81b030" 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_01a083a5-01ce-75eb-b415-0563ba88ecbd" 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_01a083a5-01ce-7323-8425-ff6b1f81b030" xlink:to="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-75eb-b415-0563ba88ecbd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a083a5-01ce-7e19-97c7-b0146b356c79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-75eb-b415-0563ba88ecbd" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a083a5-01ce-7e19-97c7-b0146b356c79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a083a5-01ce-7e19-97c7-b0146b356c79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a083a5-01ce-7e19-97c7-b0146b356c79" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a083a5-01ce-7e19-97c7-b0146b356c79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a083a5-01ce-7e4c-8e5f-385f913d55af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a083a5-01ce-7e19-97c7-b0146b356c79" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a083a5-01ce-7e4c-8e5f-385f913d55af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a083a5-01ce-7625-86b6-7e83619cbd92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a083a5-01ce-7e4c-8e5f-385f913d55af" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a083a5-01ce-7625-86b6-7e83619cbd92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-7afc-869f-279916527c50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-75eb-b415-0563ba88ecbd" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-7afc-869f-279916527c50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-7afc-869f-279916527c50_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-7afc-869f-279916527c50" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-7afc-869f-279916527c50_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-757c-b044-3fc41aa41710" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-7afc-869f-279916527c50" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-757c-b044-3fc41aa41710" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-77b4-b581-33f1d2c03aba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-757c-b044-3fc41aa41710" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-77b4-b581-33f1d2c03aba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-72b6-bfe7-6be341e545e9" 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_01a083a5-01ce-75eb-b415-0563ba88ecbd" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-72b6-bfe7-6be341e545e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-72b6-bfe7-6be341e545e9_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_01a083a5-01ce-72b6-bfe7-6be341e545e9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-72b6-bfe7-6be341e545e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-73a2-942c-d4ccabb7d1e3" 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_01a083a5-01ce-72b6-bfe7-6be341e545e9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-73a2-942c-d4ccabb7d1e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-7d16-9670-ed2041bb566a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-73a2-942c-d4ccabb7d1e3" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-7d16-9670-ed2041bb566a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_01a083a5-01ce-73c7-bd4d-6777970edc23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7323-8425-ff6b1f81b030" xlink:to="loc_us-gaap_LongTermDebtFairValue_01a083a5-01ce-73c7-bd4d-6777970edc23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_01a083a5-01ce-74e0-8b30-32ca33ee381b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7323-8425-ff6b1f81b030" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_01a083a5-01ce-74e0-8b30-32ca33ee381b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a083a5-01ce-75de-b0c1-4c19a60e43a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7323-8425-ff6b1f81b030" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_01a083a5-01ce-75de-b0c1-4c19a60e43a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount_01a083a5-01ce-7d51-9371-bd204a102682" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7323-8425-ff6b1f81b030" xlink:to="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount_01a083a5-01ce-7d51-9371-bd204a102682" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/DebtandLiquidity2018TermLoanand2018RevolvingCreditFacilityDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#DebtandLiquidity2018TermLoanand2018RevolvingCreditFacilityDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/DebtandLiquidity2018TermLoanand2018RevolvingCreditFacilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7ac1-a429-3e29303e6dad" 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_01a083a5-01ce-745c-8a4c-f656e40ad8d1" 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_01a083a5-01ce-7ac1-a429-3e29303e6dad" xlink:to="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-745c-8a4c-f656e40ad8d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a083a5-01ce-7768-8cfa-00085127e41b" 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_01a083a5-01ce-745c-8a4c-f656e40ad8d1" xlink:to="loc_us-gaap_CreditFacilityAxis_01a083a5-01ce-7768-8cfa-00085127e41b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a083a5-01ce-7768-8cfa-00085127e41b_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_01a083a5-01ce-7768-8cfa-00085127e41b" xlink:to="loc_us-gaap_CreditFacilityDomain_01a083a5-01ce-7768-8cfa-00085127e41b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a083a5-01ce-7b16-b765-1aa1197b1086" 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_01a083a5-01ce-7768-8cfa-00085127e41b" xlink:to="loc_us-gaap_CreditFacilityDomain_01a083a5-01ce-7b16-b765-1aa1197b1086" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a083a5-01ce-7478-80f1-154a84212dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a083a5-01ce-7b16-b765-1aa1197b1086" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a083a5-01ce-7478-80f1-154a84212dc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-79bf-9fd8-c9181fc74eb2" 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_01a083a5-01ce-745c-8a4c-f656e40ad8d1" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-79bf-9fd8-c9181fc74eb2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-79bf-9fd8-c9181fc74eb2_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_01a083a5-01ce-79bf-9fd8-c9181fc74eb2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-79bf-9fd8-c9181fc74eb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7d1f-bc73-9c49fd7e45fd" 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_01a083a5-01ce-79bf-9fd8-c9181fc74eb2" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7d1f-bc73-9c49fd7e45fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_A2018TermLoanFacilityMember_01a083a5-01ce-7b72-a417-b84f93f3b678" xlink:href="gti-20260930.xsd#gti_A2018TermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7d1f-bc73-9c49fd7e45fd" xlink:to="loc_gti_A2018TermLoanFacilityMember_01a083a5-01ce-7b72-a417-b84f93f3b678" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_A2018CreditAgreementMember_01a083a5-01ce-7d88-ba71-2af173837300" xlink:href="gti-20260930.xsd#gti_A2018CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-7d1f-bc73-9c49fd7e45fd" xlink:to="loc_gti_A2018CreditAgreementMember_01a083a5-01ce-7d88-ba71-2af173837300" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-730c-9975-c27196ec4c79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-745c-8a4c-f656e40ad8d1" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-730c-9975-c27196ec4c79" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-730c-9975-c27196ec4c79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-730c-9975-c27196ec4c79" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-730c-9975-c27196ec4c79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-7fa7-b8a0-60f14b209b93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-730c-9975-c27196ec4c79" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-7fa7-b8a0-60f14b209b93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a083a5-01ce-7c65-bb5c-9841a6f38537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-7fa7-b8a0-60f14b209b93" xlink:to="loc_us-gaap_LineOfCreditMember_01a083a5-01ce-7c65-bb5c-9841a6f38537" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a083a5-01ce-7da8-a6b7-5e4c05287778" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7ac1-a429-3e29303e6dad" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_01a083a5-01ce-7da8-a6b7-5e4c05287778" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a083a5-01ce-7d72-b335-1bb90ef96679" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7ac1-a429-3e29303e6dad" xlink:to="loc_us-gaap_LineOfCredit_01a083a5-01ce-7d72-b335-1bb90ef96679" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_01a083a5-01ce-7ada-81a1-0177216df144" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7ac1-a429-3e29303e6dad" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_01a083a5-01ce-7ada-81a1-0177216df144" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/InterestExpenseNarrativeDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#InterestExpenseNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/InterestExpenseNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7836-a9fb-46f2eea66167" 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_01a083a5-01ce-7398-b0ed-f240cf5a3a38" 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_01a083a5-01ce-7836-a9fb-46f2eea66167" xlink:to="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-7398-b0ed-f240cf5a3a38" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-73f4-b4aa-d7123e03bfe3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a083a5-01ce-7398-b0ed-f240cf5a3a38" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-73f4-b4aa-d7123e03bfe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-73f4-b4aa-d7123e03bfe3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-73f4-b4aa-d7123e03bfe3" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-73f4-b4aa-d7123e03bfe3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-79a8-b6b2-7dbd0c789195" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a083a5-01ce-73f4-b4aa-d7123e03bfe3" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-79a8-b6b2-7dbd0c789195" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_01a083a5-01ce-7dd7-9f90-cf03c2d48cbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a083a5-01ce-79a8-b6b2-7dbd0c789195" xlink:to="loc_us-gaap_SecuredDebtMember_01a083a5-01ce-7dd7-9f90-cf03c2d48cbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-757f-8095-eb3a08caa119" 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_01a083a5-01ce-7398-b0ed-f240cf5a3a38" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a083a5-01ce-757f-8095-eb3a08caa119" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-757f-8095-eb3a08caa119_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_01a083a5-01ce-757f-8095-eb3a08caa119" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-757f-8095-eb3a08caa119_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" 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_01a083a5-01ce-757f-8095-eb3a08caa119" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_A2023SeniorSecuredNotesMember_01a083a5-01ce-77a2-a8a8-92a60eedc5e0" xlink:href="gti-20260930.xsd#gti_A2023SeniorSecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" xlink:to="loc_gti_A2023SeniorSecuredNotesMember_01a083a5-01ce-77a2-a8a8-92a60eedc5e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_A2020SeniorSecuredNotesMember_01a083a5-01ce-707f-84dc-8b9e3f46d131" xlink:href="gti-20260930.xsd#gti_A2020SeniorSecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" xlink:to="loc_gti_A2020SeniorSecuredNotesMember_01a083a5-01ce-707f-84dc-8b9e3f46d131" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_InitialFirstLienTermLoansMember_01a083a5-01ce-7528-87f5-fdd077b3de38" xlink:href="gti-20260930.xsd#gti_InitialFirstLienTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" xlink:to="loc_gti_InitialFirstLienTermLoansMember_01a083a5-01ce-7528-87f5-fdd077b3de38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-7721-adc9-7c7004921f56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a083a5-01ce-78d3-8016-596c8bbdb1e0" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_01a083a5-01ce-7721-adc9-7c7004921f56" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_DebtModificationExpense_01a083a5-01ce-795a-91e7-34d47bb10dc5" xlink:href="gti-20260930.xsd#gti_DebtModificationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7836-a9fb-46f2eea66167" xlink:to="loc_gti_DebtModificationExpense_01a083a5-01ce-795a-91e7-34d47bb10dc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a083a5-01ce-743d-87a3-0e7eda079c52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7836-a9fb-46f2eea66167" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a083a5-01ce-743d-87a3-0e7eda079c52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a083a5-01ce-7307-9080-495a85ab3270" 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_01a083a5-01ce-7836-a9fb-46f2eea66167" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a083a5-01ce-7307-9080-495a85ab3270" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a083a5-01ce-79f4-9c8b-1ded9380a905" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a083a5-01ce-7836-a9fb-46f2eea66167" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_01a083a5-01ce-79f4-9c8b-1ded9380a905" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceLineItems_01a083a5-01ce-7198-aea8-43465a93cb65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationAllowanceLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceTable_01a083a5-01ce-72a6-aa5f-dc52103d23e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationAllowanceTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ValuationAllowanceLineItems_01a083a5-01ce-7198-aea8-43465a93cb65" xlink:to="loc_us-gaap_ValuationAllowanceTable_01a083a5-01ce-72a6-aa5f-dc52103d23e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_01a083a5-01ce-73da-a3aa-364c4ff056bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ValuationAllowanceTable_01a083a5-01ce-72a6-aa5f-dc52103d23e8" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_01a083a5-01ce-73da-a3aa-364c4ff056bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-73da-a3aa-364c4ff056bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a083a5-01ce-73da-a3aa-364c4ff056bf" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-73da-a3aa-364c4ff056bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-7612-a53c-46710db66f99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_01a083a5-01ce-73da-a3aa-364c4ff056bf" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-7612-a53c-46710db66f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_01a083a5-01ce-7d4b-a223-7be49ebf9c67" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-7612-a53c-46710db66f99" xlink:to="loc_country_US_01a083a5-01ce-7d4b-a223-7be49ebf9c67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CH_01a083a5-01ce-7906-b30d-ce5c2b13a72e" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_CH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_01a083a5-01ce-7612-a53c-46710db66f99" xlink:to="loc_country_CH_01a083a5-01ce-7906-b30d-ce5c2b13a72e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_01a083a5-01ce-7545-ad78-5b30042ad9eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowanceLineItems_01a083a5-01ce-7198-aea8-43465a93cb65" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_01a083a5-01ce-7545-ad78-5b30042ad9eb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#FairValueMeasurementsandDerivativeInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a083a5-01ce-740b-b32e-557b58a471a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:to="loc_us-gaap_DerivativeTable_01a083a5-01ce-740b-b32e-557b58a471a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7035-b016-5abf0a19b0aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a083a5-01ce-740b-b32e-557b58a471a1" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7035-b016-5abf0a19b0aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7035-b016-5abf0a19b0aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7035-b016-5abf0a19b0aa" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7035-b016-5abf0a19b0aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7501-af4b-3b69e512322b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7035-b016-5abf0a19b0aa" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7501-af4b-3b69e512322b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-75c8-bcda-dea26edee586" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7501-af4b-3b69e512322b" xlink:to="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-75c8-bcda-dea26edee586" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-74f9-8fff-9c8a7d8be521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a083a5-01ce-740b-b32e-557b58a471a1" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-74f9-8fff-9c8a7d8be521" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-74f9-8fff-9c8a7d8be521_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-74f9-8fff-9c8a7d8be521" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-74f9-8fff-9c8a7d8be521_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-78c7-bff8-4ac1c70656a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-74f9-8fff-9c8a7d8be521" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-78c7-bff8-4ac1c70656a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_01a083a5-01ce-7ddd-926b-68ef75ce4c34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-78c7-bff8-4ac1c70656a5" xlink:to="loc_us-gaap_NondesignatedMember_01a083a5-01ce-7ddd-926b-68ef75ce4c34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a083a5-01ce-779d-a32f-af599c404a0c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a083a5-01ce-740b-b32e-557b58a471a1" xlink:to="loc_srt_RangeAxis_01a083a5-01ce-779d-a32f-af599c404a0c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a083a5-01ce-779d-a32f-af599c404a0c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a083a5-01ce-779d-a32f-af599c404a0c" xlink:to="loc_srt_RangeMember_01a083a5-01ce-779d-a32f-af599c404a0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a083a5-01ce-71cf-aa24-e689b68719b2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a083a5-01ce-779d-a32f-af599c404a0c" xlink:to="loc_srt_RangeMember_01a083a5-01ce-71cf-aa24-e689b68719b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a083a5-01ce-7674-816f-d3e4dddd54a1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a083a5-01ce-71cf-aa24-e689b68719b2" xlink:to="loc_srt_MinimumMember_01a083a5-01ce-7674-816f-d3e4dddd54a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a083a5-01ce-79b7-9024-717334596555" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a083a5-01ce-71cf-aa24-e689b68719b2" xlink:to="loc_srt_MaximumMember_01a083a5-01ce-79b7-9024-717334596555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_01a083a5-01ce-7047-ba35-2949cc6b0348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_01a083a5-01ce-7047-ba35-2949cc6b0348" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_01a083a5-01ce-7903-a977-b9e208dd6fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_01a083a5-01ce-7903-a977-b9e208dd6fa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_DerivativeIneffectivenessExpense_01a083a5-01ce-7617-a96a-f9dbe75a8291" xlink:href="gti-20260930.xsd#gti_DerivativeIneffectivenessExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:to="loc_gti_DerivativeIneffectivenessExpense_01a083a5-01ce-7617-a96a-f9dbe75a8291" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTermOfContract_01a083a5-01ce-7e89-b7f4-17cb20e2bc55" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7c8e-9ee1-9a5593ea083d" xlink:to="loc_us-gaap_DerivativeTermOfContract_01a083a5-01ce-7e89-b7f4-17cb20e2bc55" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsNotionalAmountsDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#FairValueMeasurementsandDerivativeInstrumentsNotionalAmountsDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsNotionalAmountsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7144-b7c2-74d7eb6c4da5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a083a5-01ce-729a-86bb-1facb4b3aed9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7144-b7c2-74d7eb6c4da5" xlink:to="loc_us-gaap_DerivativeTable_01a083a5-01ce-729a-86bb-1facb4b3aed9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7601-8d81-bdc45f6b99cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a083a5-01ce-729a-86bb-1facb4b3aed9" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7601-8d81-bdc45f6b99cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7601-8d81-bdc45f6b99cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7601-8d81-bdc45f6b99cc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7601-8d81-bdc45f6b99cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7b55-b0cc-bb048b4d9289" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7601-8d81-bdc45f6b99cc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7b55-b0cc-bb048b4d9289" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7572-8788-3a62627c9192" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7b55-b0cc-bb048b4d9289" xlink:to="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7572-8788-3a62627c9192" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7e94-832c-f2a78b26ebc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a083a5-01ce-729a-86bb-1facb4b3aed9" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7e94-832c-f2a78b26ebc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7e94-832c-f2a78b26ebc9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7e94-832c-f2a78b26ebc9" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7e94-832c-f2a78b26ebc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7b86-aa68-37dba3b60303" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7e94-832c-f2a78b26ebc9" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7b86-aa68-37dba3b60303" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_01a083a5-01ce-71eb-bcbb-537d094f3738" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7b86-aa68-37dba3b60303" xlink:to="loc_us-gaap_NondesignatedMember_01a083a5-01ce-71eb-bcbb-537d094f3738" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a083a5-01ce-74a5-853a-c012c99c25db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7b86-aa68-37dba3b60303" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a083a5-01ce-74a5-853a-c012c99c25db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_01a083a5-01ce-75e8-8074-c9e898911e34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a083a5-01ce-7144-b7c2-74d7eb6c4da5" xlink:to="loc_us-gaap_DerivativeNotionalAmount_01a083a5-01ce-75e8-8074-c9e898911e34" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsImpactintheStatementofOperationsDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#FairValueMeasurementsandDerivativeInstrumentsImpactintheStatementofOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/FairValueMeasurementsandDerivativeInstrumentsImpactintheStatementofOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a083a5-01ce-7c3b-86f4-0c88c49e4133" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a083a5-01ce-76be-9c47-457986f511a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a083a5-01ce-7c3b-86f4-0c88c49e4133" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a083a5-01ce-76be-9c47-457986f511a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7d04-8031-d8266166a255" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a083a5-01ce-76be-9c47-457986f511a8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7d04-8031-d8266166a255" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7d04-8031-d8266166a255_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7d04-8031-d8266166a255" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7d04-8031-d8266166a255_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7f00-a2ff-1db6b1d3d3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7d04-8031-d8266166a255" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7f00-a2ff-1db6b1d3d3bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7836-a53a-9051493c9adf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7f00-a2ff-1db6b1d3d3bc" xlink:to="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7836-a53a-9051493c9adf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7c45-86ab-2d2772e44f78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_01a083a5-01ce-76be-9c47-457986f511a8" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7c45-86ab-2d2772e44f78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7c45-86ab-2d2772e44f78_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7c45-86ab-2d2772e44f78" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7c45-86ab-2d2772e44f78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7135-8745-9b2e48dbdffe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7c45-86ab-2d2772e44f78" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7135-8745-9b2e48dbdffe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a083a5-01ce-79eb-b424-d2004ca6b15b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7135-8745-9b2e48dbdffe" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_01a083a5-01ce-79eb-b424-d2004ca6b15b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_01a083a5-01ce-7aeb-a8fd-1a3d604c9971" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01a083a5-01ce-7c3b-86f4-0c88c49e4133" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_01a083a5-01ce-7aeb-a8fd-1a3d604c9971" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/FairValueMeasurementsandDerivativesInstrumentsNotDesignatedasHedgesDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#FairValueMeasurementsandDerivativesInstrumentsNotDesignatedasHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/FairValueMeasurementsandDerivativesInstrumentsNotDesignatedasHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_01a083a5-01ce-7a0b-85b5-70f06de44894" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_01a083a5-01ce-7a0b-85b5-70f06de44894" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7578-ba6c-ef6d44ed985b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_01a083a5-01ce-7a0b-85b5-70f06de44894" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7578-ba6c-ef6d44ed985b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7578-ba6c-ef6d44ed985b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7578-ba6c-ef6d44ed985b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7578-ba6c-ef6d44ed985b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7fe1-a9b0-8c7abd32535c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7578-ba6c-ef6d44ed985b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7fe1-a9b0-8c7abd32535c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7c72-82ca-0716e5ab94f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7fe1-a9b0-8c7abd32535c" xlink:to="loc_us-gaap_ForeignExchangeContractMember_01a083a5-01ce-7c72-82ca-0716e5ab94f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7a82-a669-44033dd780af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_01a083a5-01ce-7a0b-85b5-70f06de44894" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7a82-a669-44033dd780af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7a82-a669-44033dd780af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7a82-a669-44033dd780af" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7a82-a669-44033dd780af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7f2d-80d4-05847ca2bea2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a083a5-01ce-7a82-a669-44033dd780af" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7f2d-80d4-05847ca2bea2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_01a083a5-01ce-7592-a7cd-c24420d61a39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a083a5-01ce-7f2d-80d4-05847ca2bea2" xlink:to="loc_us-gaap_NondesignatedMember_01a083a5-01ce-7592-a7cd-c24420d61a39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_01a083a5-01ce-7b81-a89b-6394c4ea41aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_01a083a5-01ce-7b81-a89b-6394c4ea41aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_01a083a5-01ce-781a-97bf-f7a17550ceb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_01a083a5-01ce-781a-97bf-f7a17550ceb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeNet_01a083a5-01ce-7146-ab4c-42b5da8f684a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeNet_01a083a5-01ce-7146-ab4c-42b5da8f684a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a083a5-01ce-7e9a-9a01-716149fba056" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_01a083a5-01ce-7940-b4e8-65b9cf4cc424" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a083a5-01ce-7e9a-9a01-716149fba056" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#AccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/AccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a083a5-01ce-7c78-967d-539ee3bea304" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a083a5-01ce-7c78-967d-539ee3bea304" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a083a5-01ce-7c78-967d-539ee3bea304" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-73a5-9cad-3ae38d3be639" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a083a5-01ce-7dc2-9dd8-fe4087a6c47b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-73a5-9cad-3ae38d3be639" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_01a083a5-01ce-7394-a926-5cd7f3299288" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a083a5-01ce-73a5-9cad-3ae38d3be639" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_01a083a5-01ce-7394-a926-5cd7f3299288" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a083a5-01ce-73f4-8de4-52486cfa6c91" 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_AccumulatedOtherComprehensiveIncomeLossTable_01a083a5-01ce-7c78-967d-539ee3bea304" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a083a5-01ce-73f4-8de4-52486cfa6c91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-73f4-8de4-52486cfa6c91_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_01a083a5-01ce-73f4-8de4-52486cfa6c91" xlink:to="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-73f4-8de4-52486cfa6c91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-723e-a47d-c1707739de63" 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_01a083a5-01ce-73f4-8de4-52486cfa6c91" xlink:to="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-723e-a47d-c1707739de63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_01a083a5-01ce-7b2c-b724-90d3a9bf7012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-723e-a47d-c1707739de63" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_01a083a5-01ce-7b2c-b724-90d3a9bf7012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_01a083a5-01ce-7998-8b7e-50bcde392fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a083a5-01ce-723e-a47d-c1707739de63" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_01a083a5-01ce-7998-8b7e-50bcde392fdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a083a5-01ce-7ccb-8bf9-e760823476d6" 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_01a083a5-01ce-723e-a47d-c1707739de63" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a083a5-01ce-7ccb-8bf9-e760823476d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7ec8-839b-683fd6aaef93" 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_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a083a5-01ce-7ec8-839b-683fd6aaef93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a083a5-01ce-7b0e-a3db-7d0b51feefc4" 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_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_StockholdersEquity_01a083a5-01ce-7b0e-a3db-7d0b51feefc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_01a083a5-01ce-74e1-b766-3f99dfa864b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_01a083a5-01ce-74e1-b766-3f99dfa864b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_01a083a5-01ce-7e57-8565-e9ea72b48f74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_01a083a5-01ce-7e57-8565-e9ea72b48f74" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_01a083a5-01ce-79c7-b328-e6c1a9436c51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_01a083a5-01ce-79c7-b328-e6c1a9436c51" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_01a083a5-01ce-73ef-a86d-531f51e72797" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_01a083a5-01ce-73ef-a86d-531f51e72797" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a083a5-01ce-71fe-a5e2-49de29c71b16" 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_AccumulatedOtherComprehensiveIncomeLossLineItems_01a083a5-01ce-7248-b29d-8433dfcc7ddc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a083a5-01ce-71fe-a5e2-49de29c71b16" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a083a5-01ce-736a-ba6a-c09fb8841def" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/LossEarningsperShareDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#LossEarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/LossEarningsperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a083a5-01ce-766e-bbf8-bfd368d9632f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a083a5-01ce-766e-bbf8-bfd368d9632f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7de0-9d9a-110238ba1ef5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a083a5-01ce-766e-bbf8-bfd368d9632f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7de0-9d9a-110238ba1ef5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7de0-9d9a-110238ba1ef5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7de0-9d9a-110238ba1ef5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7de0-9d9a-110238ba1ef5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-760a-bc7c-160a07e60bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7de0-9d9a-110238ba1ef5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-760a-bc7c-160a07e60bb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7d57-9a43-af953055622c" xlink:href="gti-20260930.xsd#gti_OutOfTheMoneyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-760a-bc7c-160a07e60bb4" xlink:to="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7d57-9a43-af953055622c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_InTheMoneyMember_01a083a5-01ce-7fab-b960-157d672d6b27" xlink:href="gti-20260930.xsd#gti_InTheMoneyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-760a-bc7c-160a07e60bb4" xlink:to="loc_gti_InTheMoneyMember_01a083a5-01ce-7fab-b960-157d672d6b27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7f79-9471-2569440eba84" 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_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_NetIncomeLoss_01a083a5-01ce-7f79-9471-2569440eba84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a083a5-01ce-7ae3-b01a-c9d38bf10345" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a083a5-01ce-7ae3-b01a-c9d38bf10345" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a083a5-01ce-7c86-a266-438474bae27f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a083a5-01ce-7c86-a266-438474bae27f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_01a083a5-01ce-7d24-be40-c77c235dce35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_EarningsPerShareBasic_01a083a5-01ce-7d24-be40-c77c235dce35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_01a083a5-01ce-7e3f-9872-a800e56dd306" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_EarningsPerShareDiluted_01a083a5-01ce-7e3f-9872-a800e56dd306" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a083a5-01ce-7b95-93b1-bf6c0cd5c78e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a083a5-01ce-7183-90be-eb1aab74d152" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a083a5-01ce-7b95-93b1-bf6c0cd5c78e" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/StockBasedCompensationDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#StockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/StockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" 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_01a083a5-01ce-775d-9979-895a7667608a" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a083a5-01ce-7971-9a76-7204ba749d7f" 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_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_AwardTypeAxis_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7971-9a76-7204ba749d7f_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_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7971-9a76-7204ba749d7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" 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_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_DeferredShareUnitsMember_01a083a5-01ce-7b0d-9155-73d4852cd618" xlink:href="gti-20260930.xsd#gti_DeferredShareUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_gti_DeferredShareUnitsMember_01a083a5-01ce-7b0d-9155-73d4852cd618" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a083a5-01ce-71a8-af36-70dd6384a248" 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_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a083a5-01ce-71a8-af36-70dd6384a248" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_CommonStockPurchaseWarrantMember_01a083a5-01ce-7f0b-becd-441fc9b6d5c3" xlink:href="gti-20260930.xsd#gti_CommonStockPurchaseWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_gti_CommonStockPurchaseWarrantMember_01a083a5-01ce-7f0b-becd-441fc9b6d5c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a083a5-01ce-723d-b10a-e7610de5e780" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a083a5-01ce-723d-b10a-e7610de5e780" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-714b-80f0-4745a3684747_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:to="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-714b-80f0-4745a3684747_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:to="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a083a5-01ce-7bf0-aa07-edce439676cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a083a5-01ce-7bf0-aa07-edce439676cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a083a5-01ce-7cda-8dde-4185f3dda924" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a083a5-01ce-7cda-8dde-4185f3dda924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7174-99b4-e80c30215810_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7174-99b4-e80c30215810_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7223-8c78-fb3ab0e8803f" xlink:href="gti-20260930.xsd#gti_OutOfTheMoneyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:to="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7223-8c78-fb3ab0e8803f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a083a5-01ce-70bd-b200-f7e015a0a3aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a083a5-01ce-70bd-b200-f7e015a0a3aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a083a5-01ce-71a7-9ab5-86bf61ce1119" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a083a5-01ce-71a7-9ab5-86bf61ce1119" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a083a5-01ce-7da3-93e1-ae329ebf63f4" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a083a5-01ce-7da3-93e1-ae329ebf63f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a083a5-01ce-7345-b4da-e8294b1aedf7" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a083a5-01ce-7345-b4da-e8294b1aedf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a083a5-01ce-7fe4-8b1c-607c1f4f0283" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a083a5-01ce-7fe4-8b1c-607c1f4f0283" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a083a5-01ce-75bd-aace-177d96b2616a" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a083a5-01ce-75bd-aace-177d96b2616a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/StockBasedCompensationDetails_1" xlink:type="simple" xlink:href="gti-20260930.xsd#StockBasedCompensationDetails_1"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/StockBasedCompensationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" 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_01a083a5-01ce-775d-9979-895a7667608a" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a083a5-01ce-7971-9a76-7204ba749d7f" 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_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_AwardTypeAxis_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7971-9a76-7204ba749d7f_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_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7971-9a76-7204ba749d7f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" 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_01a083a5-01ce-7971-9a76-7204ba749d7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_DeferredShareUnitsMember_01a083a5-01ce-7b0d-9155-73d4852cd618" xlink:href="gti-20260930.xsd#gti_DeferredShareUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_gti_DeferredShareUnitsMember_01a083a5-01ce-7b0d-9155-73d4852cd618" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a083a5-01ce-71a8-af36-70dd6384a248" 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_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a083a5-01ce-71a8-af36-70dd6384a248" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_CommonStockPurchaseWarrantMember_01a083a5-01ce-7f0b-becd-441fc9b6d5c3" xlink:href="gti-20260930.xsd#gti_CommonStockPurchaseWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a083a5-01ce-7748-bb90-1e95cca50f9e" xlink:to="loc_gti_CommonStockPurchaseWarrantMember_01a083a5-01ce-7f0b-becd-441fc9b6d5c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-714b-80f0-4745a3684747_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:to="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-714b-80f0-4745a3684747_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_01a083a5-01ce-714b-80f0-4745a3684747" xlink:to="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a083a5-01ce-7bf0-aa07-edce439676cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_01a083a5-01ce-7bf0-aa07-edce439676cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a083a5-01ce-7cda-8dde-4185f3dda924" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_01a083a5-01ce-7871-9a5a-a095af54f959" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_01a083a5-01ce-7cda-8dde-4185f3dda924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a083a5-01ce-775d-9979-895a7667608a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7174-99b4-e80c30215810_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-7174-99b4-e80c30215810_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_01a083a5-01ce-7174-99b4-e80c30215810" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7223-8c78-fb3ab0e8803f" xlink:href="gti-20260930.xsd#gti_OutOfTheMoneyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_01a083a5-01ce-732f-9094-d228cf07e528" xlink:to="loc_gti_OutOfTheMoneyMember_01a083a5-01ce-7223-8c78-fb3ab0e8803f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a083a5-01ce-70bd-b200-f7e015a0a3aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a083a5-01ce-70bd-b200-f7e015a0a3aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a083a5-01ce-71a7-9ab5-86bf61ce1119" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a083a5-01ce-71a7-9ab5-86bf61ce1119" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a083a5-01ce-7da3-93e1-ae329ebf63f4" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a083a5-01ce-7da3-93e1-ae329ebf63f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a083a5-01ce-7345-b4da-e8294b1aedf7" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a083a5-01ce-7345-b4da-e8294b1aedf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a083a5-01ce-7fe4-8b1c-607c1f4f0283" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_01a083a5-01ce-7fe4-8b1c-607c1f4f0283" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a083a5-01ce-75bd-aace-177d96b2616a" 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_01a083a5-01ce-784e-8eb2-9959967057d5" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01a083a5-01ce-75bd-aace-177d96b2616a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.graftech.com/role/RestructuringandRelatedActivitiesDetails" xlink:type="simple" xlink:href="gti-20260930.xsd#RestructuringandRelatedActivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.graftech.com/role/RestructuringandRelatedActivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a154f0-a149-73c0-a411-76dbf1aa8f09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a154f0-a149-73c0-a411-76dbf1aa8f09" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a154f0-a149-7dd8-bbe2-107102f26170" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a154f0-a149-73c0-a411-76dbf1aa8f09" xlink:to="loc_srt_RangeAxis_01a154f0-a149-7dd8-bbe2-107102f26170" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a154f0-a149-7dd8-bbe2-107102f26170_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a154f0-a149-7dd8-bbe2-107102f26170" xlink:to="loc_srt_RangeMember_01a154f0-a149-7dd8-bbe2-107102f26170_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a154f0-a149-75fc-b1dc-275b24301293" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a154f0-a149-7dd8-bbe2-107102f26170" xlink:to="loc_srt_RangeMember_01a154f0-a149-75fc-b1dc-275b24301293" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a154f0-a149-7ddd-8bb4-22cc1f9464c9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a154f0-a149-75fc-b1dc-275b24301293" xlink:to="loc_srt_MinimumMember_01a154f0-a149-7ddd-8bb4-22cc1f9464c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a154f0-a149-7f7d-918f-2d4d70180c37" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a154f0-a149-75fc-b1dc-275b24301293" xlink:to="loc_srt_MaximumMember_01a154f0-a149-7f7d-918f-2d4d70180c37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_01a154f0-a149-716a-a418-d26204506579" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_01a154f0-a149-73c0-a411-76dbf1aa8f09" xlink:to="loc_us-gaap_RestructuringPlanAxis_01a154f0-a149-716a-a418-d26204506579" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_01a154f0-a149-716a-a418-d26204506579_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_01a154f0-a149-716a-a418-d26204506579" xlink:to="loc_us-gaap_RestructuringPlanDomain_01a154f0-a149-716a-a418-d26204506579_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_01a154f0-a149-7219-b6ee-f21a5e5995b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_01a154f0-a149-716a-a418-d26204506579" xlink:to="loc_us-gaap_RestructuringPlanDomain_01a154f0-a149-7219-b6ee-f21a5e5995b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gti_MexicoCityClosureMember_01a154f0-a149-7c68-ba25-f9acd738849a" xlink:href="gti-20260930.xsd#gti_MexicoCityClosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_01a154f0-a149-7219-b6ee-f21a5e5995b1" xlink:to="loc_gti_MexicoCityClosureMember_01a154f0-a149-7c68-ba25-f9acd738849a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_01a14a92-ecb6-7789-a0ce-d1ff40dfabfb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_SeveranceCosts1_01a14a92-ecb6-7789-a0ce-d1ff40dfabfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_01a14a94-0996-7b2a-9f97-6e3750a68fdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_01a14a94-0996-7b2a-9f97-6e3750a68fdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_01a14a94-a864-7af1-8f45-4f963a2d1762" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_RestructuringCharges_01a14a94-a864-7af1-8f45-4f963a2d1762" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_01a154da-8aec-730c-9e5e-cfe3335dd965" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_RestructuringReserve_01a154da-8aec-730c-9e5e-cfe3335dd965" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_01a154dc-35d0-704c-b8cf-894bd8a2a944" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostIncurredCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_01a154dc-35d0-704c-b8cf-894bd8a2a944" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_01a154dc-fce5-764a-8b9b-642944e77b25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_PaymentsForRestructuring_01a154dc-fce5-764a-8b9b-642944e77b25" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_01a154f0-a149-717f-bf16-5b4c87d361d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_01a154f0-a149-70f0-91fb-9fc7a35b6914" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_01a154f0-a149-717f-bf16-5b4c87d361d1" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
