Background: There is increasing evidence of the need for treatment engagement between Persons with Severe Mental Illnesses (PwSMIs) and Mental Health Professionals (MHPs). This therapeutic process involves collaborative work between patients and MHPs, which improves the condition. Community nurses are uniquely positioned to facilitate this process as they act as the focal point of interaction between patients and the health system. Methods: This qualitative study explored the community nurses’ experiences in treatment engagement with PwSMI through eight group interviews of 35 community nurses from District Mental Health Programs (DMHPs) across Karnataka (South India) from February 2020 to March 2020. The audio recordings of the interviews were transcribed and coded to arrive at themes and subthemes. Results: The major themes identified were factors influencing treatment engagement, strategies to tackle treatment nonengagement, and challenges in dealing with nonengagement. The reasons for nonengagement were lack of insight and lack of knowledge of sociocultural, logistic, and treatment-related factors. The DMHP teams contacted patients through phone calls, home visits, and liaisons with health workers and intervened with them through education and depot injections. The major challenges were difficulty conducting home visits, distances, the unavailability of medications, and the need for adequate infrastructure and human resources. Conclusion: Community nurses address a few factors of nonengagement, such as insight, sociocultural factors, and treatment-related factors. Addressing the systemic challenges and adequate training of nurses in intervening in the dropped-out PwSMIs would help to reduce the treatment gap.