Background Diabetes prevalence is increasing rapidly in Bangladesh, and there is an urgent need to promote preventive behaviours for type 2 diabetes, such as maintaining a healthy body weight, eating healthily, avoiding tobacco and being active for 150 minutes per week. Methods We used a qualitative methodology informed by the capability, opportunity, motivation theory of behaviour change to explore the factors affecting physical activity among men and women in rural Bangladesh. We conducted semi-structured interviews and focus group discussions with 64 purposively sampled participants with and without diabetes, and five health workers. From the results of descriptive content analysis, we identified key capabilities, opportunities and motivations to engage with in our mHealth and community mobilization interventions. Results Men and women without diabetes lacked awareness about the need to remain physically active to prevent diabetes, and most felt that their activity levels were sufficient. Housework was not commonly perceived as physical activity among all respondents. These knowledge and capability gaps could be addressed through mHealth messaging and community mobilization providing information on sufficiency and types of physical activity to prevent and control diabetes. Men were physically active while working outside the home, whereas women felt unsafe and conspicuous, and were constrained by family commitments and social expectations of appropriate behaviour. Women engaged in strategies to protect their own and their family’s reputations. These opportunity factors affecting physical activity indicated the need for strategies developed through participatory processes to challenge unhealthy gender norms and increase women’s safety. Conclusion Formative research data can enable the development of contextually relevant interventions. Data show that mHealth interventions should consider gendered barriers to physical activity, tailoring information to meet men’s and women’s needs, and that community mobilization interventions should enable unhealthy, gendered community norms to be challenged. Participatory interventions can enable communities to push the boundaries of socially acceptable behaviours to increase physical activity, helping to prevent and control diabetes.