People with serious mental illness (SMI) and/or substance use disorders (SUDs) have an elevated risk of premature mortality compared to the general population. This has been attributed to higher rates of chronic illness among these individuals, but also to inequities in healthcare access and treatment. Integrated care has the potential to improve the health of people with SMI/SUDs by removing barriers to healthcare access and enhancing quality of care. The aims of this scoping review are to: 1) identify empirical investigations of interventions designed to integrate care for people with SMI/SUDs, 2) describe the underlying theories, models, and frameworks of integrated care that informed their development, and 3) determine the degree to which interventions address dimensions of a comprehensive and validated framework of integrated care. Guidelines for best practice and reporting of scoping reviews will be followed using the framework of Arksey and O’Malley and the PRISMA-ScR checklist. An iterative and systematic search of peer-reviewed publications reporting empirical research findings will be conducted. This literature will be identified by searching five databases: Medline (Ovid), PsycINFO, CINAHL, Embase (Ovid), and Scopus. Publications will be eligible for inclusion if they evaluate interventions specifically designed to integrate care (either across or within services) for people with SMI/SUDs. Two reviewers will independently screen publications in two successive stages of title and abstract screening, followed by full text screening of remaining publications. A tabular summary and narrative synthesis will be completed using data extracted from each included study. A directed content analysis will also be conducted, with descriptions of interventions mapped against a theoretical framework of integrated care. This review will identify the extent and nature of empirical investigations evaluating interventions to integrate care for people with SMI/SUDs. A team of relevant stakeholders, including people with lived experience of mental health conditions, mental health professionals, other health professionals, and researchers from a range of disciplines, has been established. This team will be engaged throughout the review and will ensure that the findings are widely disseminated.