Objective The mental health challenges facing people who care for somebody with cancer are well documented. While many support interventions focus on provision of information or cognitive behavioural therapy, the literature suggests that psychosocial interventions could also be of value, especially given the low social support frequently reported by carers. Singing is a psychosocial activity shown to improve social support, increase positive emotions, and reduce fatigue and stress. This study explored whether weekly group singing can reduce anxiety, depression and well-being in cancer carers over a 6-month period. Design A multisite non-randomised longitudinal controlled study. Setting The Royal Marsden National Health Service Trust in Greater London. Participants 62 adults who currently care for a spouse, relative or close friend with cancer who had not recently started any psychological therapy or medication. Interventions On enrolment, participants selected to join a weekly community choir for 12 weeks (n=33) or continue with life as usual (n=29). Outcome measures The primary outcome was mental health using the Hospital Anxiety and Depression Scale. The secondary outcome was well-being using the Warwick Edinburgh Mental Wellbeing Scale. Using linear mixed effects models, we compared the change in mental health and well-being over time between the two groups while adjusting for confounding variables including demographics, health-related variables, musical engagement and length of time caring. Results Participants in the choir group showed a significantly greater decrease in anxiety over time than participants in the control group (B=-0.94, SE=0.38, p=0.013) and a significantly greater increase in well-being (B=1.25, SE=0.49, p=0.011). No changes were found for depression. Sub-group analyses showed carers with anxiety or below-Average well-being were most likely to benefit. Conclusions This study builds on previous research showing the mental health benefits of singing for people with cancer by showing that weekly singing can also support anxiety and well-being in cancer carers.