Psychosocial interventions play a key role in addressing mental health and substance use needs for children and adolescents living in low- and middle-income countries (LMICs). While research efforts have primarily focused on their effectiveness, implementation outcomes also require examining. We conducted a systematic review of qualitative, quantitative, and mixed-methods studies (PROSPERO: CRD42022335997) to synthesize the literature on implementation outcomes for psychosocial interventions for children and adolescents in LMICs. We searched Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, Web of Science, PsychINFO, and Global Health through April 2023. Data were extracted and quality appraised through the Mixed Methods Appraisal Tool (MMAT) independently by two reviewers. A total of 13,380 records were screened, and 87 studies met inclusion criteria. Feasibility was the most reported implementation outcome (69, 79%), followed by acceptability (60, 69%), and fidelity (32, 37%). Appropriateness was assessed in 11 studies (13%), implementation costs in 10 (11%), and sustainability in one (1%). None of the included studies reported on penetration or adoption. Despite a growing body of evidence for implementation research in child and adolescent global mental health, most research focused on earlier-stage implementation outcomes, assessing them in research-controlled settings. To overcome this, future efforts should focus on assessing interventions in routine care, assessing later-stage implementation outcomes through standardized tools.