Socioeconomic consequences of pension reforms have often been discussed without careful consideration of institutional contexts, despite the fact that institutional designs of public pensions differ substantially across countries. This study argues that the outcomes of pension reforms vary depending on the institutional structure of public pensions, by showing that the associations between public pension spending and old-age employment rates of different socio-demographic groups vary across different institutional contexts. Using time-series cross-section data from 20 European countries and the United States from 1998 to 2019, the study examines how changes in public pension spending ‘per older person’, a comparable measure for the welfare state effort towards old-age income security, are associated with gender- and education-specific employment rates in old age. The study also explores how these associations differ under different pension regimes, constructed based on the degree to which financing and benefit structures exhibit redistributive orientations. The results reveal complex gender and educational gradients in the relationship between public pension spending and old-age employment. Female employment rates, especially among the low-educated, are more sensitive to changes in pension spending in the ‘Beveridgean’ regime that focuses on basic income security. In the Bismarckian regime characterized by earnings-related pensions, educational differences in the marginal effects on male employment rates are, in particular, larger. Future pension reforms balancing the goal of activation and social equity should therefore consider the longstanding institutional design of public pensions.