The cognitive benefits of a greater sense of control are well-established; however, only recently have the mechanisms involved in this relationship been explored. Because of its well-established cognitive benefits and positive relationship to perceived control, physical activity has been suggested as a potential mediator. However, with age, not only does cognition tend to decline, but so does one’s perception of control and their level of physical activity. Therefore, it is important to understand the relationship between these variables from a life span perspective. The goal of the current study was to expand on past work that investigated physical activity as a mediator between perceived control and change in cognition across 4 years to a multi-decade perspective that examines these variables as they change from midlife to older adulthood. To do so, we used longitudinal data across 20 years from the Midlife in the United States Study. Our results show that perceiving more control over one’s life predicted less decline in cognition 20 years later, and this relationship was mediated by an increase in physical activity. We consider limitations and future directions to further our understanding of the role of physical activity in the relationship between perceived control and cognitive aging.