Academics and policymakers have suggested making flexible work arrangements (FWAs) the default in workplaces to promote a family-friendly workplace culture conducive to having and raising children. However, systematic research investigating how FWAs, as a long-term approach to negotiating work–family spheres, are related to fertility among dual-earner heterosexual couples is limited. Drawing on the linked-lives perspective, we theorize the relationship between FWAs and fertility among couples and potential variation depending on the interplay of both spouses’ work and family characteristics. We test our hypotheses using longitudinal couple-level dyadic data in the United Kingdom (2010–2022). We find that although FWA availability alone is unrelated to fertility, wives’ (not husbands’) FWA use is significantly associated with a higher probability of experiencing a first birth. Moreover, the effect of wives’ FWA use is particularly pronounced when both spouses work in professional and managerial occupations and when husbands contribute a larger proportion of income and at least equal housework. This study reveals a gendered effect of FWAs on fertility across work–family arrangements, deepening our understanding of couple-level dynamics in the fertility process.