Background: Advanced cancer affects people's lives, often causing stress, anxiety and depression. Peer mentor interventions are used to address psychosocial concerns, but their outcomes and effect are not known. Our objective was to determine the feasibility of delivering and investigating a novel peer mentor intervention to promote and maintain psychological wellbeing in people with advanced cancer. Methods: A mixed methods design incorporating a two-armed controlled trial (random allocation ratio 1:1) of a proactive peer mentor intervention plus usual care, vs. usual care alone, and a qualitative process evaluation. Peer mentors were recruited, trained, and matched with people with advanced cancer. Quantitative data assessed quality of life, coping styles, depression, social support and use of healthcare and other supports. Qualitative interviews probed experiences of the study and intervention. Results: Peer mentor training and numbers (n = 12) met feasibility targets. Patient participants (n = 12, from 181 eligible who received an information pack) were not recruited to feasibility targets. Those who entered the study demonstrated that intervention delivery and data collection were feasible. Outcome data must be treated with extreme caution due to small numbers, but indicate that the intervention may have a positive effect on quality of life. Conclusions: Peer mentor interventions are worthy of further study and researchers can learn from these feasibility data in planning participant recruitment and data collection strategies. Pragmatic trials, where the effectiveness of an intervention is tested in real-world routine practice, may be most appropriate. Peer mentor interventions may have merit in enabling survivors with advanced cancer cope with their disease.