Abstract Background ACE (Active, Connected, Engaged) is a theory-informed, pragmatic intervention using peer volunteering support to promote active ageing in socially disengaged, inactive older adults. This study aimed to establish ACE’s feasibility and acceptability. Methods Fifty-four older adults were recruited as either peer volunteers (activators; n = 15) or participants (ACEs; n = 39). Participants were randomized to one-to-one support from an activator (ACEs-Intervention [ACEs-I]) or a waiting-list control group (ACEs-Control [ACEs-C]). Activators supported ACEs-I to get out more and engage with local activities. Objectively measured physical activity (PA), lower limb function, and number of out of house activities were assessed at baseline and post-intervention. A mixed-methods process evaluation assessed changes in confidence to get out and about, social support, autonomy, competence, and relatedness. Results Eighty-two percent of ACEs (mean age = 73.7 years [SD 7.3]) and all activators completed assessments at both baseline and post-intervention (6 months). ACEs-I reported more out of house activities (M [SD] = 6.34 [4.15]). ACEs-I increased physical function post-intervention (M [SD] = 9.8 [2.3]). ACEs-I reported improved well-being and vitality and increased confidence to get out and about, confidence in the face of specific barriers, knowledge of local initiatives, and perceived social support post-intervention. Activators, although sufficiently active at baseline, increased their PA further. ACE was well-accepted and easy to deliver. Conclusions ACE is an acceptable and feasible intervention for helping socially disengaged older people to get out and about more, improve their confidence, and engage more with their community.