Access to high-quality, on-time medical care, including care for mental health conditions, is a fundamental human right. This case study shares the journey of Ventura County Behavioral Health (VCBH) toward defining, standardizing, and operationalizing an innovative, state-sponsored mental health care model—the Full Service Partnership (FSP)—to increase access to essential care for the most vulnerable county residents. It outlines how Third Sector helped Ventura County to harness the potential of FSPs and implement changes to processes, service provision, and data use. The lessons presented in this case study should be beneficial to furthering national efforts to obtain better outcomes for individuals with symptoms of severe and persistent mental illness.