AIMS: Diabetes is two to three times more prevalent in people with severe mental illness, yet little is known about the challenges of managing both conditions from the perspectives of people living with the co-morbidity, their family members or healthcare staff. Our aim was to understand these challenges and to explore the circumstances that influence access to and receipt of diabetes care for people with severe mental illness. METHODS: Framework analysis of qualitative semi-structured interviews with people with severe mental illness and diabetes, family members, and staff from UK primary care, mental health and diabetes services, selected using a maximum variation sampling strategy between April and December 2018. RESULTS: In all, 39 adults with severe mental illness and diabetes (3 with type 1 diabetes and 36 with type 2 diabetes), nine family members and 30 healthcare staff participated. Five themes were identified: (a) Severe mental illness governs everyday life including diabetes management; (b) mood influences capacity and motivation for diabetes self-management; (c) cumulative burden of managing multiple physical conditions; (d) interacting conditions and overlapping symptoms and (e) support for everyday challenges. People living with the co-morbidity and their family members emphasised the importance of receiving support for the everyday challenges that impact diabetes management, and identified barriers to accessing this from healthcare providers. CONCLUSIONS: More intensive support for diabetes management is needed when people's severe mental illness (including symptoms of depression) or physical health deteriorates. Interventions that help people, including healthcare staff, distinguish between symptoms of diabetes and severe mental illness are also needed.