Background: Communities of Practice (CoPs) are increasingly used in health and non-health sectors globally. Evidence suggests that CoPs can support health promotion activities, but the research mainly encompasses formal, professional contexts: the role and contribution of CoPs in community-centred health promotion has not been explored. This paper presents a process evaluation of a CoP that aimed to facilitate social innovation among voluntary, community, faith and social enterprise (VCFSE) organisations. Hosted by a city-region government in England, VCFSE organisations were invited to join a CoP to enable the development and implementation of their ideas for addressing gambling harms., Methods: The process evaluation sought to develop mid-level programme theory for the use of CoPs in community-centred health promotion. Data collection consisted of 33 qualitative interviews with stakeholders, as well as project reporting. Data were organised using a framework approach which supported the construction of themes and a complex intervention model. The research team reflected on these to develop the programme theory., Results: The CoP facilitated the development of community-centred interventions for addressing gambling harms through a two-track process: first, a community of VCFSE staff was formed, whose understanding of gambling harms was nurtured through discussions led by people with Lived Experience; second, the CoP contributed to project development via collaboration, knowledge sharing and an integrated referral pathway, although project-level benefits were uneven. Learning was generated in community engagement, training, education, support and social campaigns., Conclusions: The findings confirm the combined effectiveness of a CoP, varied VCFSE projects and people with Lived Experience to co-create an evolving knowledge-base for a city-region government's gambling harms reduction strategy. CoPs may therefore complement partnership working in community settings, although additional training support may be required in comparison with CoPs involving health professionals. The city-region government's approach could be replicated in other emerging public health areas., Competing Interests: Declaration of conflicting interestsThe authors declare that they have no conflicting interests: TM, JE, CJ, JG, PR, JW and SS have not previously received research funding from the gambling industry, either directly or indirectly. TM has worked as a researcher on various NIHR-funded health service and public health projects over the past five years, including most recently PHIRST South Bank. CJ is an Early Career Researcher attached to PHIRST South Bank: their PhD, completed in 2023, was funded by a London South Bank University scholarship.JE and JG have no past research funding to report. JE’s role in gambling harms reduction at GMCA is funded by Gambling Commission regulatory settlement money. JG works for the charity ‘Gambling with Lives’ which has previously received regulatory settlement money from the Gambling Commission for service development: JG’s participation in the research was funded via the PHIRST South Bank NIHR grant.Besides her work with PHIRST South Bank, PR has received funding for three NIHR projects in the past five years to evaluate digital mental health platforms and mental health service use in inpatient and community child and adolescent services. She has also received funding from the Wellcome Trust and St. Andrew’s Healthcare. JW and SS have, over the past five years, received funding for diverse research, commissioned and educational projects from Public Health England, Health Education England, National Health Service England, European Regional Development Fund, Burdett Trust for Nursing and NIHR.