Abstract Background The ABCs for Mental Wellbeing study aims to improve mental health and wellbeing by adopting, implementing and evaluating a universal, community-based mental health promotion intervention model in Finland. The study gathers information and experiences of the implementation processes, identifies barriers and facilitators, and best practices for the implementation, and the feasibility and contextual adaptability of the intervention in different settings and specific target groups. Methods The implementation took place in four municipality community settings. In total, 40 participants attended the ABC activities. The study employs a mixed methods approach to look at the implementation processes: a quantitative survey before and after the implementation, and qualitative interviews with the employees implementing the model and the participants involved with the ABC activities. Results Based on qualitative analysis, the most identified facilitator is management support alongside the competencies of professionals. The observed effects of group activities aligned with the ABC model on mental wellbeing show that participants not only experienced the benefits of model-compliant activities on their mental wellbeing but also increased their awareness of factors influencing their mental wellbeing. The results of the quantitative analysis will be ready during the spring. Conclusions The study offers fresh insights into the obstacles and enablers affecting the implementation of a mental health promotion intervention model. The best practice strategies and guidelines identified are being shared both nationally and internationally and utilised to enhance future programme implementation and adaptation of these practices in various settings. Key messages • Best practice strategies and guidelines for successful implementation of mental health promotion identified. • The ABCs for Mental Wellbeing increased participants’ awareness of the factors influencing their mental wellbeing.