Mental health issues among young people are increasing and many young people will require support. Mentoring programmes are an effective strategy for the development of positive health and well-being in young people. Evidence suggests that peers have more influence in altering young people’s behaviour than adults, and adolescent peer-to-peer mentoring programmes are becoming more common. However, there is little evidence to support the effectiveness of these programmes in terms of mentor outcomes. This literature review examined mentor outcomes of peer-to-peer mentoring as an intervention for young people. The review aimed to identify published evaluations of peer-to-peer mentoring, describe the characteristics of the included studies, critique the methodological quality, and describe the reported strengths and limitations in the existing evidence to inform future interventions. The review highlighted the limited literature on mentor outcomes but provides some evidence that young mentors can be effective in providing positive mentoring to their peers.