Available evidence shows that brief, supervised high intensity interval training programs improve a range of outcomes with cancer survivors. However, maintenance of exercise beyond a supervised exercise phase remains poor. This randomised controlled trial will evaluate the influence of a structured peer support program on exercise adherence and the maintenance of cardiorespiratory fitness and quality of life for 12 months in cancer survivors, following a four week supervised high intensity interval training (HIIT) intervention. Breast, colorectal or prostate cancer survivors (n=244) will complete a four week supervised HIIT intervention before being randomly assigned to either a ‘peer support group’ or ‘no peer support’ group for 12 months. All participants will have free access to a gym, and be encouraged to accumulate either 150 minutes of moderate exercise or 75 minutes of vigorous exercise each week (i.e., to meet the current exercise oncology guidelines). Peer supporters (cancer survivors who have also completed the four week HIIT and undergone training to provide them with the skills to help motivate and assist their partners) will help maintain exercise in those assigned to them. VO2peak, quality of life and exercise levels will be assessed for all participants before and immediately after the four week intervention and again at three, six and twelve months. Results from this study will inform clinical practice and provide a framework for implementing peer support programs into the community to improve health outcomes for cancer survivors.