Objective: This study investigated whether the association between adolescents’ lifestyle types and depression is mediated by body mass index (BMI) and body image. Methods: The sample comprised 1,243 eighth-grade adolescents who participated in the 15th wave (2022) of the Panel Study on Korean Children. Participants were classified into four lifestyle types based on their sleep duration, physical activity, and media use. Path analysis was conducted to examine the relationships among lifestyle types, BMI, body image, and depression. Results: First, adolescents with unhealthy lifestyle types reported significantly higher levels of depression than those with a healthy lifestyle type. Second, BMI did not mediate the association between lifestyle types and depression. Third, the indirect effect of lifestyle types on depression through body image was significant across all unhealthy lifestyle types. Finally, the sequential mediation effect of lifestyle types on depression through BMI and body image was not significant; however, BMI exerted a significant indirect effect on depression through body image. Conclusions: The study findings indicate that adolescents’ lifestyle imbalance and body image play important roles in depression. These results indicate that interventions for adolescent mental health should move beyond selective approaches targeting high-risk groups to incorporate universal strategies aimed at improving daily lifestyle patterns and promoting positive body image.