Physical activity might be a viable tool for enhancing mental wellbeing because, in general, physical activity has been found to be related to more positive affect and higher satisfaction with life. The way we think, feel, and act changes with age, so it may be that physical activity, wellbeing, and the link between physical activity and wellbeing change with age too. Without consideration for developmental changes, study findings are decontextualized and difficult to translate into people’s lives. Aiming to become better equipped to use physical activity as a tool to intervene with wellbeing, we explored a lifespan perspective of physical activity and wellbeing. In this review, we (1) discuss physical activity, wellbeing, and the link between physical activity and wellbeing at different life stages, (2) highlight the need to consider interpersonal and intrapersonal differences in these constructs, and (3) identify gaps in the literature that, if filled, would further enhance our understanding of physical activity and wellbeing across the lifespan.