Grandparents play an increasingly central role in childcare across advanced industrialized societies, yet their contribution is highly gendered: grandmothers are significantly more likely than grandfathers to provide care, reflecting persistent gendered divisions of labor that extend into later life. While substantial research has examined how parenthood affects political participation—often showing that the opportunity costs of child-rearing reduce mothers’ political engagement more than fathers’—little is known about whether similar “spillover” effects extend to grandparents. Drawing on cross-sectional data from 25 European countries in the European Social Survey, this study investigates how the transition to first-time grandparenthood influences political participation among men and women. We argue that, analogous to parents, grandparents face time and caregiving constraints that can reduce their political engagement, generating a gendered effect. Using a comparative perspective, we examine whether the arrival of a first grandchild differentially affects the propensity to vote and engage in political activities among grandmothers versus grandfathers. Our findings aim to extend theories of the resource model of political participation by highlighting the intergenerational transmission of opportunity costs and the overlooked role of older adults in shaping democratic engagement.