Drawing on public opinion and empirical research, one may advise people to participate in voluntary organizations because voluntary participation can improve their mental health and social well-being. However, do such benefits apply across different types of participation and across the life course? In this study, we investigated whether benefits to mental health and social well-being differ between nonpolitical and political participation and across age groups (preregistration is accessible at https://osf.io/kqcbe). Using 25 waves of data from the British Household Panel Survey and the Understanding Society (1991–2016), we conducted multilevel analyses with observations nested within participants in younger (14–29, n = 10,536), middle-aged (40–50, n = 4,955), and older (65–75, n = 3,059) adults. We used life satisfaction and GHQ-12 scores as measures of mental health, and social support and neighborhood belonging as measures of social well-being. We found only few and small significant effects at the within-person level: On occasions when younger adults reported political participation, they reported slightly higher neighborhood belonging than when they did not. On occasions when older adults reported nonpolitical or political participation, they reported slightly higher life satisfaction than when they did not. However, we found no significant differences between nonpolitical and political participation and among age groups. In sum, our findings qualify the opinion that voluntary participation yields significant benefits to engaged individuals. We discuss potential explanations, including characteristics of political participation in the United Kingdom.