This is the protocol for a Campbell systematic review. The objectives are as follows. The primary aim of this mixed methods review is to synthesise the available evidence regarding the effectiveness of restorative justice interventions (RJIs) for reducing offending and reoffending outcomes in children and young people. We are also particularly interested in the impact of RJIs on children and young peoples' violent offending and violent reoffending. A second aim of the review is to examine whether the magnitude of effectiveness of RJIs may be influenced by study characteristics such as the population (e.g., age, ethnicity, or sex), the form of intervention (e.g., face‐to‐face mediation compared to family group conferencing), the place of delivery of the intervention (e.g., in independent office, in court), implementation (e.g., trained facilitators, dose, fidelity) and methodology (e.g., randomised controlled trial). The third aim of the review is to synthesise the qualitative evidence about RJ to develop a better contextual understanding of how these programmes may work and to elucidate factors that might increase the efficacy and implementation of RJ interventions. The specific research questions this systematic review aims to address are: (1) Do RJ interventions reduce children and young people's involvement in offending or reoffending relative to a comparison group? [RQ1]. (2) Is there variation in the impact of different RJ approaches on young people's involvement in offending or reoffending? [RQ2]. (3) Is there variation in the impact of RJIs on children and young people's offending or reoffending depending on the characteristics of the participants taking part in the RJI (e.g., sex, age, ethnicity)? [RQ3]. (4) What characteristics of RJIs, influence the effectiveness of RJIs for children and young people's offending and reoffending? [RQ4]. (5) What are the most notable barriers and facilitators, as reported by participants (e.g., the victims, children/young people, or mediators who have taken part in an evaluation of an RJI, or those children or young people who were meant to take part in an evaluation but ultimately did not), to the implementation of RJIs to reduce later offending or reoffending? [RQ5].