This narrative review examines the literature on credible messenger mentoring (CMM) as an intervention to promote the health and well-being of youth involved in the juvenile legal system. In the CMM model, individuals with shared life experiences (e.g., from the same neighborhoods or marginalized communities, with former gang or incarceration history) serve as mentors, leveraging their own history of transformation to engage youth involved in the juvenile legal system and promote individual and community change. CMM is an increasingly popular approach for working with youth involved in the juvenile legal system, yet the state of the research on this intervention is unclear. This article provides a narrative review of existing research on CMM to understand what is known, and unknown, about the intervention. Results find an emerging, but incomplete body of evidence supporting the impact of CMM for youth involved in the juvenile legal system, and for adult mentors. Qualitative and observational findings provide stronger support for the model, while quantitative findings provide more mixed evidence, indicating that CMM may be a promising life course health intervention, yet needs more empirical study. Findings from this review underscore the value of integrating community-informed evidence in the evaluation of health interventions. Future research can inform contemporary interest in the CMM approach and guide implementation and measurement standards for optimizing intervention delivery with youth involved in the juvenile legal system.