We share insights on community governance and participatory dynamics in CoAct for Mental Health, an initiative within the CoAct European project that explored citizen social science understood as participatory research co-designed and directly driven by citizen groups sharing a social concern. Awarded the 2024 European Union Prize for Citizen Science in the Digital Communities category, the initiative co-designed a chatbot featuring micro-stories of social support from adults with lived mental health experiences and their families. The effort was carried out with the involvement of institutional representatives from the mental health governance system. We detail how the diverse interests of these actors were translated into the project’s design and implementation, and we analyse some of the scientific results obtained that would not have been achievable without their collective involvement. Emphasizing co-researcher participation throughout, we illustrate the development of participatory research practices in this sensitive and complex context.