Background <p>Men’s lower life expectancy has been in part attributed to adherence to masculine stereotypes restricting health promoting behaviors. Health-specific self-efficacy beliefs are theorised to contribute to these outcomes and recent research suggests addressing the link between masculinity and these beliefs is a key pathway to men’s health promotion. Gender-sensitised health interventions show promise for helping men overcome health barriers as the “safe space” provides opportunity to broaden perspectives of masculinity, contributing to increases in health self-efficacy, which then mediates improved health outcomes. This study aimed to address gaps in previous research by examining this mechanism of gender-sensitised health promotion longitudinally in an intervention context.</p> Methods <p>A sample of 295 men participating in the Sons of the West (SOTW) 2019 program, a 10-week gender-sensitised, community-based health program, were measured pre-program and post-program to longitudinally assess changes in health outcomes. Regression analyses were used to test a mediation model of health behavior change.</p> Results <p>Findings showed improvements in health behavior, health self-efficacy, psychological distress, and decreased conformity to masculine norms. Residualized scores of the changes from pre-intervention to post-intervention indicated the changes in health self-efficacy fully mediated the relationship between changes in conformity to masculine norms and changes in health behavior and psychological distress.</p> Conclusions <p>Results suggest the key mechanism of change was the provision of opportunities for men to negotiate masculine stereotypes thus increasing health self-efficacy and explaining health improvements. This study utilized data from a real-world, large-scale men’s health program but was limited to two waves of data. Future research and implications are discussed.</p>