Purpose: framed within the life course and ecological perspectives, this study investigated the association between earlier-life individual and contextual socioeconomic conditions and later-life physical activity. The mediating role of later-life characteristics was also examined.<br/><br/>Methods: contemporary and historical Census data as well as three bi-annual waves of nationally representative panel data from the Understanding America Study (N=1,981) were used. Three types of physical activity were separately assessed: mild, moderate, and vigorous, to understand the effect of earlier-life circumstances on different types of physical activity over the life course. Multilevel growth curve models were used to address the research questions.<br/><br/>Results: a higher level of father’s education in respondents’ earlier life was associated with higher levels of mild (OR=1.13, p&lt;.05) and moderate (OR=1.25, p&lt;.001) physical activity in respondents’ later life. Growing up in a higher-poverty area was associated with lower levels of moderate (OR=0.95, p&lt;.05) and vigorous (OR=0.95, p&lt;.05) physical activity in later life. Better health status before the age of 16 was associated with a slower decline (OR=1.05, p&lt;.05) in moderate physical activity in later life. The associations between other earlier-life circumstances and later-life physical activity were largely mediated by later-life characteristics.<br/><br/>Discussion: findings underscore the long-term ramifications of earlier-life circumstances for later-life physical activity, emphasizing that human development is shaped by a confluence of individual and contextual conditions throughout the life course. Study findings suggest that interventions to promote physical activity at older ages would benefit from a perspective that takes into account the individual and contextual circumstances over the life course.