A large body of research supports the role of the therapeutic alliance in predicting positive change in psychotherapy. This systematic review examined determinants of alliance quality and its association with treatment outcomes in an under-served and under-researched population—justice-involved youth—with whom several challenges and contextual considerations arise that bear relevance to the alliance. The search strategy yielded 23 independent studies meeting eligibility criteria and describing diverse treatments: 14 quantitative records synthesized narratively and nine qualitative studies that underwent thematic analysis. A complex picture emerged, precluding firm conclusions about factors linked to enhanced alliances and the alliance–outcome relationship with justice-involved youth. Nevertheless, some promising findings were noted across quantitative studies, including potential treatment benefits related to alliance growth and creating positive alliances with caregivers. The review also highlighted the potential relevance of the young person’s relationships with peers and parents and their treatment readiness and expectations to alliance quality. Drawing on adolescent, caregiver, and therapist perspectives, the thematic synthesis of qualitative studies generated themes related to key elements of constructive alliances and their role in creating a foundation for initiating change. An integrated discussion is provided, highlighting practical implications and suggestions for addressing methodological limitations and substantive knowledge gaps.