Background: People who experience Severe Mental Illness (SMI) often have low levels of physical activity, high levels of sedentary behaviour, poor diet, and sleep problems. These factors are linked to worse mental health symptoms, lower wellbeing, greater hopelessness, lower quality-of-life, and physical health-related diseases, including cardiovascular disease, stroke, hypertension, osteoarthritis, cancer, chronic obstructive pulmonary disease, obesity, and diabetes, contributing to 15 -20 years reduced life expectancy. Purpose/Aim: This study investigates the impact of Well-Track healthy lifestyle intervention in SMI, it addresses the question: "What is the effect of Well-Track on mental wellbeing and sleep quality/insomnia for SMI patients?". Methods: An open-label patient cohort design with no control group. Pre-intervention, 4-week and 8-week intervention assessments using participant self-report measures: Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) and Sleep Conditioning Index (SCI). Participants were seventy-six Community Mental Health Team (CMHT) participants, 35 males and 41 females, with an age range of 20 -65, and average age of 41 years. An eight-week intervention: a free-to-keep wearable tracker (instructions, set up, and access to apps), exercise, diet and sleep hygiene advice, a motivational interview and goal-setting session and two follow-up support sessions with a health coach. Results: WEMWBS scores significantly improved, from 37.52 (SD 10.18) to 42.35 (SD 7.14) at 4 weeks and to 44.06 (SD 6.03) at 8 weeks, with large effect sizes. SCI scores significantly improved, from 12.03 (SD 7.29) to 15.45 (SD 8.00) at 4 weeks and to 17.26 (SD 8.12) at 8 weeks, with large effect sizes. Conclusion: Well-Track was integrated into a SMI physical health check service and was found to be beneficial in terms of improving wellbeing and sleep quality and