Objectives: Research shows that social participation is beneficial for overall health and well-being. Yet, no research to our knowledge has examined whether social participation is associated with greater marital satisfaction in middle-aged and older couples. We hypothesized that middle-aged and older adults would have greater marital satisfaction when their spouse engaged in social groups because there would be greater opportunity for self-expansion and for social support from ties outside the marriage. Methods: We used background self-report data from a multi-method study of 98 middle-aged and older adult married couples ( N = 196) with chronic conditions. As part of the study, spouses completed questionnaires that measured the frequency and intensity of involvement in social groups (e.g., church, business groups). Marital satisfaction was measured with the Locke Wallace Marital Adjustment Test. Results: Contrary to our hypotheses, results from actor–partner interdependence models provided no evidence that one’s own social participation was associated with one’s own marital satisfaction (actor effects). However, in line with our hypotheses regarding partner effects, one spouse’s (a) report of any social participation with church organizations, business groups, or social groups, (b) greater number of affiliations with different organizations, (c) greater frequency of participation, and (d) being an active officer in a social organization were significantly associated with the other spouse’s greater marital satisfaction. Discussion: Findings of this study suggest that having a spouse who participates in social groups is good for relationship satisfaction in mid to late life marriage.