Higher levels of academic education are associated with higher levels of physical activity throughout the lifespan. However, the mechanisms underlying this association are unclear. Cognitive functioning is a potential mediator of this association because higher levels of education are associated with better cognitive function, which is related to greater engagement in physical activity. Here, we used large-scale longitudinal data from 105,939 adults 50 years of age or older (55% women) from the Survey of Health, Ageing, and Retirement in Europe to investigate whether initial status and change in cognitive function mediate the relationship between education and change in physical activity. Education and physical activity were self-reported. Cognitive function was assessed based on delayed recall and verbal fluency. Academic education was assessed at the first measurement occasion. The other measures were collected seven times between 2004 and 2019. The mediating role of cognitive function was tested using longitudinal mediation analyses combined with growth curve models. We found that higher levels of education were associated with higher levels and slower decreases in cognitive function, which in turn predicted a lower decrease in physical activity across time. These results support the presence of an indirect effect of education on physical activity trajectories by affecting the intercept and slope of cognitive function. Specifically, these findings suggest that both the initial status and change in cognitive function mediate the association between academic education and change in physical activity. In addition, results revealed that, across the aging process, differences in cognitive function and physical activity widen between the low and high educated. In other words, this study demonstrates the long-lasting effect of education on cognitive function and physical activity. (PsycInfo Database Record (c) 2023 APA, all rights reserved).