Exercise participation motives are differentially associated with engagement in physical activity (PA), with some reasons for exercise promoting, and others deterring behaviour. Perceptions of the body may account for these differential associations. Drawing from embodied theories of body image, motives that orient attention towards the body's function may promote PA, whereas motives focused on appearance may deter PA. The goal of this research was to examine various dimensions of body image as mediators between participation motives and engagement in moderate-to-vigorous PA (MVPA), after controlling for age, sex, and body mass index (BMI). Participants (N = 470, nfemale = 210; Mage = 36; SDage = 11) completed an online survey that assessed their motives for physical activity (i.e., fitness, interest/enjoyment, social, competence, and appearance motives), values and satisfaction associated with appearance and functionality dimensions of body image, and engagement in MVPA. The overall model accounted for 33% of the variance in MVPA. Fitness motives were directly associated with MVPA (B = 3.44, CI = 0.984 to 5.90) while satisfaction with body functionality was a significant mediator between interest/enjoyment motives and MVPA (B = 0.129, CI = 0.050 to 0.227) and appearance motives and MVPA (B = -0.029, CI = -0.069 to -0.002). Focusing on the functioning of the body is associated with engaging in PA at levels commensurate for health benefits. Engaging in MVPA because it is interesting/enjoyable rather than for appearance reasons may facilitate satisfaction with the functioning of one's body which in turn is associated with engagement in MVPA.