Aim To design, implement and evaluate a nurse-led capacity building intervention (PromoGOB) for intersectoral action for health at local governments. Design The programme was based on theories of the policy process and organizational change and facilitated by a nurse developing a health broker role. A complex intervention perspective was adopted in carrying out the study. The intervention was evaluated using a mixed method embedded design. Methods Quantitative component relied on a specific questionnaire. This tool, designed and piloted ad hoc, measured the capacity in terms of knowledge, awareness, resources, skills, and commitment, both at sectoral and government levels. For the qualitative component, semi-structured interviews were conducted. These explored the perceived capacity and feasibility and acceptability issues. The programme was initiated at the end of October 2019, and it lasted a total of 5 weeks. Nineteen individuals representing various sectors at a local government in northern Spain participated in the study. The data analysis was concluded by the end of March 2020. Findings PromoGOB positively influenced participants' capacity for addressing health promotion. Awareness component, intersectoral work and the nurse as health broker were essential in the programme. The necessity of political participation was identified as an issue to be prioritized in future studies. Conclusion This study highlights the relevance of capacity building at local governments and the role that nurses can play in it. Further work should be undertaken to continue developing Health in All Policies approach at local level. Impact This study offers a starting point for nurses to get involved in the policy process of health promotion, performing a specific role as health brokers, building capacity at local governments for addressing social determinants of health, and delving into theories and concepts of the Health in All Policies field.