Mental health or well-being provides individuals with an enhanced agentic capacity for formal volunteering. However, this capacity may be realized more effectively through the structural resources for volunteering provided by education. Analyzing white respondents from the 1995-2005 National Survey of Midlife Development Panel Study (N = 1,431), we examine the contingent effects of mental well-being and education on the probability of formal volunteering. In longitudinal models, we find that mental well-being has a role in volunteering only at higher levels of education and that deficits in mental well-being reduce the effect of education. This holds across three representative indicators of mental well-being capturing the absence of negative symptoms as well as the presence of thriving or positive emotion. As a whole, our findings suggest that agency and structure are intertwined in determining who volunteers.