This study investigated the effects of mindfulness and exercise training on indicators of mental health and stress by examining shared mediators of program effects. Community-recruited adults ( N = 413) were randomized into one of three conditions: (a) mindfulness-based stress reduction, (b) moderate intensity exercise, or (c) wait-list control. Composite indicator structural equation models estimated direct, indirect, and total effects. Results showed that mindfulness-based self-efficacy fulfilled a prominent role in mediating meditation and exercise program effects. Findings suggest that mindfulness and exercise training share similar mechanisms that can improve global mental health, including adaptive responses to stress.