Children and adolescents with obesity are at higher risk of developing depression and anxiety, and adolescent dieting is a risk factor for the development of depression. Therefore, determining the psychological effect of obesity treatment interventions is important to consider. To investigate the association between obesity treatment interventions, with a dietary component, and the change in symptoms of depression and anxiety in children and adolescents with overweight/obesity. Searches of MEDLINE, Embase, Cochrane Library, and PsychINFO were conducted from inception to August 2018. Hand searching of references was conducted to identify missing studies. Obesity treatment interventions, with a dietary component, conducted in children and adolescents (age <18 years) with overweight/obesity, and validated assessment of depression and/or anxiety were included. Data were independently extracted by 1 reviewer and checked for accuracy. Meta-analysis, using a random-effects model, was used to combine outcome data and moderator analysis conducted to identify intervention characteristics that may influence change in depression and anxiety. The meta-analyses were finalized in May 2019. Change in symptoms of depression and anxiety postintervention and at the latest follow-up. Of 3078 articles screened, 44 studies met inclusion criteria with a combined sample of 3702 participants (age range, 5.6 to 16.6 years) and intervention duration of 2 weeks to 15 months. Studies reported either no change or a statistically significant reduction in symptoms of depression or anxiety. Meta-analyses of 36 studies found a reduction in depressive symptoms postintervention (standardized mean difference [SE], -0.31 [0.04]; P < .001), maintained at follow-up in 11 studies at 6 to 16 months from baseline (standardized mean difference [SE], -0.25 [0.07]; P < .001). Anxiety was reduced postintervention (10 studies; standardized mean difference [SE], -0.38 [0.10]; P < .001) and at follow-up (4 studies; standardized mean difference [SE], -0.32 [0.15]; P = .03). Longer intervention duration was associated with a greater reduction in anxiety (R2 = 0.82; P < .001). Higher body mass index z score at baseline was associated with a greater reduction in depression (R2 = 0.19; P = .03). Structured, professionally run pediatric obesity treatment is not associated with an increased risk of depression or anxiety and may result in a mild reduction in symptoms. Treatment of weight concerns should be considered within the treatment plan for young people with depression and obesity.