This study investigated the processes associated with the engagement of adults aged 70 years and older in a 12-month long research-based structured exercise programme. A sample of 21 participants (Mean age (SD) 75.8 (3.9); 14 females) and six exercise class leaders or researchers involved in the programme participated in individual semi-structured interviews. Transcripts were analysed with the principles of interpretive qualitative analysis. Our findings suggest that a programme that runs locally, provides individual attention/tailoring, delivers meaningful benefits, offers a staged approach to efficacy building, creates a sense of ownership, and provides intergenerational support and opportunities for social interaction, facilitates exercise engagement in later life.