Policymakers and practitioners in health promotion (e.g. those working for local, state or federal government organisations or community and non-government organisations with a focus on health and wellbeing) are increasingly interested in citizen science as a means of involving the public in research and decision making. The potential benefits of citizen science approaches in health promotion include increased research capacity, incorporation of community perspectives on problems and solutions, and improved public awareness and acceptance of actions to improve health. However, health promotion practitioners and policymakers report having limited familiarity and experience with citizen science and a desire to build their capacity in these approaches. The Citizen Science in Prevention (CSP) project aims to build capacity for citizen science in health promotion by: 1) supporting the development and implementation of citizen science projects by policymakers and practitioners, 2) establishing a network of health promotion stakeholders with familiarity and interest in citizen science approaches, and 3) co-designing resources to support the use of citizen science in policy and practice contexts. A comprehensive mixed methods evaluation will establish the reach, satisfaction, and impacts that can be attributed to the capacity building intervention. This paper describes the first known initiative to build capacity in the application of citizen science approaches in health promotion and we hope that this work will assist others in the development and implementation of capacity building activities for citizen science in health promotion and beyond.