Aims: To map existing research-based knowledge of everyday life and illness management among people with coexisting type 2 diabetes and severe mental illness, and to identify study designs, aims, populations and themes. Methods: A systematic literature search was performed on 16 April 2019 using Medline, Embase, PsycINFO, Cinahl, the Cochrane Library, and the Web of Science to conduct a scoping review. Included studies were summarized with regard to the quantity of research, the study designs, aims, populations and themes. Results: From 3406 records, we included 23 studies about everyday life and illness management among people with coexisting type 2 diabetes and severe mental illness. Four studies were qualitative (observations, interviews and focus groups), and 19 were quantitative (observational and interventions) and used questionnaires. Five themes emerged in the findings: (1) diet and exercise, but not other diabetes self-care activities, are consistently compromised in the target group; (2) psychiatric exacerbation diminishes diabetes self-care; (3) social support and high self-efficacy improve diabetes self-care; (4) use of healthcare services is compromised; and (5) quality of life and well-being is poor. Conclusions: The limited research into the studied population’s experiences with coexisting type 2 diabetes and severe mental illness is characterized by its heterogeneity in aims and methods and a strong focus on diabetes management and treatment. Further research focusing on the management of both conditions in everyday life is needed to improve specialized and integrated care targeting the population.