Objectives: People with severe mental illness (SMI) have a 2- to 3-fold higher risk of developing type 2 diabetes (DM), an increased risk of subsequent DM complications, higher mortality and poorer health-related quality of life. Although mental health professionals have an important role in supporting people with SMI in diabetes management, their primary focus is often on mental health, not physical conditions. Few studies have investigated patients’ experiences of living with coexisting SMI and DM to identify their needs for diabetes support from mental health professionals. Methods: Semistructured interviews were conducted with 15 adults with SMI and DM. Interviews were transcribed and analyzed using systematic text condensation. Results: Five themes emerged from the data: 1) mental illness overshadows diabetes management, 2) mental state substantially influences diabetes care, 3) daily diabetes routines are challenging to maintain, 4) diabetes is burdensome and 5) dialogue about diabetes with mental health professionals is infrequent. Conclusions: Self-managing DM is extremely complex for patients who also live with SMI. Diabetes care is strongly influenced by emotional and mental states and the ability to establish daily routines. A need exists to enhance support from mental health professionals to improve DM self-management among people with mental illness. The present findings can inform the development of tailored interventions to support people with mental illness in DM self-management.