Regular exercise can be beneficial for people living with a severe mental illness. By better understanding the perspectives and challenges of adults with severe mental illness who are engaged in exercise, we can enhance the design and implementation of exercise programs to better support their mental health and recovery. Nineteen adults (aged 19-73 years) were recruited from transdiagnostic mental health services and local disability services in Western Australia. Patients had engaged in structured exercise services within last 6 months as part of the treatment and/or management of their mental illness. Thematic analysis was used to understand participants' experiences and health outcomes. Participants described themes relating to their exercise experience including establishment of human connection, routine and purpose, and emotional experiences in exercise. Exercise engagement was perceived to improve acute and sustained mental health effects, and behavioural replacement. Patients reported better symptom management, replacing harmful behaviours with positive ones, and reported gains in overall physical health and personal strength. Our findings demonstrate the importance of incorporating the voice of those with lived experience to better understand how exercise impacts their health, treatment, and recovery outcomes. This research has provided valuable insights for clinicians and researchers to develop sustainable client-centred interventions, that may improve health outcomes for this population.