Lifestyle-related behaviours-such as sedentary behaviour, physical inactivity, poor nutrition, disrupted sleep and substance use-are increasingly recognised as important factors in the onset and persistence of mental illness. Evidence for the efficacy and cost-efficiency of lifestyle interventions in mental health is growing, and such approaches are now embedded in international guidelines and endorsed by major health organisations and associations as 'lifestyle psychiatry'. Nevertheless, despite this progress, these interventions remain underused in mental healthcare and support. One contributing factor is the lack of a shared conceptual understanding of 'lifestyle psychiatry', which risks fragmented practice, inconsistency in research and uncertainty around its role in policy, care and support. This paper presents a conceptual framework for lifestyle psychiatry, developed through an iterative, collaborative process involving 43 contributors across 15 countries, representing clinical, academic, policy and lived experience expertise. The framework defines core domains, outlines key challenges to behaviour change specific to mental health populations and emphasises multilevel and equity-oriented approaches. It aligns with person-centred and recovery-oriented care and serves as a shared reference point for practical application and future development. With this, we aim to support the structured, context-sensitive integration of lifestyle psychiatry into mental healthcare and support.