Youth with severe obesity are vulnerable to body dissatisfaction. Extracurricular activity (ECA) involvement has been linked to positive social interactions and body image in community samples; however, these links remain to be tested in clinical samples of youth with severe obesity. The present study explored ECA involvement [both physical and nonphysical activities (PAs)] in a clinical sample of youth with obesity to determine whether ECA involvement was related to body image (appearance and weight esteem) and social life (, social experiences with peers). Participants were 209 adolescents (Mean age = 15.05; 50.2% female) who completed a baseline assessment at a tertiary care weight management program. Of the participants, 70.3% of youth reported participating in PAs, and 56.5% reported participating in non-PAs. As hypothesized, weight esteem and social life were higher in those who participated in PA vs. those who did not. Mediation analyses revealed that social life positively mediated the relationship between PA participation and weight esteem. Social life may be a mechanism by which PA participation is positively related to weight esteem in youth with severe obesity. Findings could inform weight management programs for youth with obesity who are at risk for social inclusion and body dissatisfaction.