Severe mental disorder (SMD) produces a significant functional limitation that affects the performance of daily activities. The occupational therapist intervenes on this limitation by seeking greater autonomy of these patients through specific activities. This study aims to identify the main limitations of people with SMD and to examine whether an occupational intervention has any effect in helping to overcome or ameliorate these limitations. A quasi-experimental study including 103 participants was carried out. An evaluation using the World Health Organization Disability Assessment Schedule (WHODAS 2.0) questionnaire was performed before and after the intervention. Within the activity program, those with a higher attendance rating during cognitive stimulation, cooking workshop, therapeutic walks, relaxation, and creative activities were mainly men. Both patients and professionals indicated that Understanding and Communicating, Participation in Society, and Activities of Daily Living were the main perceived limitations. Upon discharge, patients and professionals reported positive outcomes. The intervention programs carried out by occupational therapy, along with the other aspects of the treatment that SMD patients received, played an important part in improving the performance and occupational interests of these patients.