Background/Objectives: The prevalence of Diabetes Mellitus (DM) is a major concern in Saudi Arabia, making it a challenge for health delivery for those with severe mental illness (SMI). This study aims to explore the barriers to access and utilization of diabetes care among patients with diabetes and serious mental illnesses, their relatives, and healthcare providers to provide evidence-based recommendations for health policy improvement. Methods: A qualitative interpretive research design was used via Braun and Clarke's framework to analyze the data thematically. Semi-structured interviews were conducted with 35 participants, including patients, relatives, and healthcare providers between September and October 2023, in Jeddah city, Saudi Arabia. Results: The following four themes emerged from the qualitative data: (1) The status of integrated care, (2) Barriers to access to diabetes care at different levels, (3) Navigating obstacles to providing comprehensive diabetes care, and (4) Evidence-based recommendations for health policy improvement. Conclusions: This study underscores the necessity for a comprehensive and integrated approach to care, educational programs, specialized clinics, and improved healthcare logistics. Integrating mental health and diabetes management is needed to ensure better utilization.