Severe Mental Illnesses (SMI) significantly affect physical and mental health, with individuals often facing isolation, stigma, and reduced life expectancy. While evidence supports that physical activity (PA) can be beneficial for individuals with SMI, there is limited research on the practical considerations needed when designing these PA programmes to ensure safe and supportive experiences. This collaborative study, with a mental health charity, explores the experiences of 21 stakeholders (coaches, volunteers, development officers) who deliver community-based PA for individuals with SMI. Qualitative data collection included observations (N = 10 sessions, mean= >12hrs), semi-structured interviews (21 participants), and informal conversations. Reflexive thematic analysis was used to craft three themes: (a) The Challenge of Initiating Physical Activity in a Novel Community Environment, (b) Approaches to Supporting Service Users in Entering PA Spaces: Setting Expectations and Creating Safe Spaces, (c) Continued Participation: Approaches to Maintain PA Engagement. Results illustrate the value of experiential knowledge in creating practices that are both trauma-informed and support long-term recovery.