Treatment non-adherence in mental illness leads to a host of negative consequences, including early mortality. In this context, the present paper ascertains the causes of mortality among persons with mental illness who were non-adherent to their treatment from a community mental health center in India. It is a retrospective research design, and the survey method of sampling was followed. A home visit was carried out, and collateral information was obtained from various sources to ascertain the causes of mortality. A matrix method has been adopted to explain the profile of the mortality persons. In 5 years, out of 178 persons, 9 (5.05%) have died for various reasons. The deceased persons’ average life expectancy was 43.33 ± 14.24 years; 66.7% were male, 44.4% were abandoned or institutionalized by their caregivers, nearly 77.2% had multiple comorbidities, and had not received treatment for both psychiatric and other health conditions. Deterioration of health, heart attack, chronic obstructive pulmonary disease, suicide, accident, and falling into the water due to seizures were the causes of mortality. Formal and informal community mental health services must be strengthened to ensure treatment adherence and improve the life expectancy of persons with mental illness.