Introduction: Emergency service workers (e.g. police, fire, ambulance officers) are regularly exposed to occupational stressors and potentially traumatic events, resulting in an increased risk of poor mental and physical health. For example, emergency service workers are twice as likely to experience suicidal thoughts compared to the general population and one in ten will develop posttraumatic stress disorder. Despite this, emergency service workers face barriers to accessing traditional mental healthcare. Physical activity is non-stigmatising and may help improve the mental and physical health of this population; however, novel ways to help people engage are needed. Peers with lived experience may be well-placed to co-deliver physical activity programs alongside health professionals. The aim of this study was to understand the experiences of peer-facilitators co-delivering an online physical activity intervention for emergency service workers and their families. Methods: Qualitative interviews were conducted with 6 peer-facilitators. Interviews were audio recorded, transcribed, and analysed using exploratory thematic analysis. Results: Two main themes were explored. The first theme related to the value of lived experience that reflected two subthemes, i) credibility and relatedness by virtue of experience; and ii) knowledge and confidence by virtue of experience. The second theme related to the impact of the peer-facilitator role on the peers themselves, whereby peer-facilitators reported an increased sense of purpose and social connection. Discussion: This qualitative study provides insights into how peer-facilitators can complement health professionals in the delivery of physical activity interventions for emergency service workers. Further research is needed to elucidate training requirements and safety protocols.