Theoretical considerations suggest that volunteering contributes to retirement adjustment because it compensates for role losses following retirement. However, the idea that mental health benefits of volunteering are stronger after retirement than prior to retirement has been hardly tested empirically. Moreover, it remains open to question who benefits from volunteering in retirement in particular. In this study, I investigated whether trajectories of volunteering were associated with concurrent trajectories of life satisfaction (general life satisfaction, satisfaction with leisure time) across the retirement transition, and whether life satisfaction at and prior to retirement moderated these associations after retirement. I conducted multivariate latent growth curve modeling using panel data (N = 9,043) from the German Socio-Economic Panel (SOEP; 1984–2019). Slopes of volunteering and life satisfaction were split into one preretirement slope and two postretirement slopes (short- and long-term after retirement). Slopes of life satisfaction were regressed on concurrent slopes of volunteering. Increases in volunteering were related to concurrent increases in general life satisfaction after retirement, but not before. The associations after retirement were more positive than the associations prior to retirement. There were no such differences for satisfaction with leisure time. Associations between slopes of volunteering and life satisfaction after retirement were the more positive the lower the level of life satisfaction at retirement and the stronger the decrease in life satisfaction prior to retirement. These findings imply that volunteering may compensate for the loss of the working role, particularly for retirees who experienced decreases in life satisfaction in the retirement transition.