The physical health disparities experienced by people who live with mental illness are well documented. This population group has cardiometabolic risks and diseases at rates 1·4–2·0 times higher than people without mental illness, and physical health conditions are responsible for 70% of the deaths of people with severe mental illness. They are the major drivers of the 13–15 year reduction in life expectancy that is found in individuals with mental illness, compared with those without mental illness. The 2019 The Lancet Psychiatry Commission: a blueprint for protecting physical health in people with mental illness brought these disparities into focus and provided guidance for health promotion, multiprofessional clinical care, and future research. Lifestyle risk factors, such as high smoking rates, low physical activity, high levels of sedentary behaviour, low cardiorespiratory fitness, lower diet quality, detrimental eating behaviour, and poor sleep hygiene, are prevalent in this population. Lifestyle interventions that target these risk factors are effective adjunctive therapies in people living with mental illness, alleviating mental health symptoms while protecting physical health and promoting wellbeing. Given the established benefits of lifestyle interventions in mental health settings, there is a need to shift the focus from efficacy towards implementation research and address how best to implement and deliver lifestyle interventions as core clinical practice. Implementation should include a recognition of the social and economic context in which behavioural risk factors emerge to ensure equity of outcomes.