Background: The purpose of this paper was to identify personal, social, and environmental mediators of recreational physical activity (PA) in a 6-month netball-based intervention for women and girls in Tonga. Methods: Tonga Netball’s “low-engagement village program” was implemented in 10 villages and aimed to increase the recreational PA levels in women and girls through a comprehensive, structured community-level netball program addressing key barriers to participation. In a mixed-methods approach, these mediating barriers were identified through qualitative interviews based on the socioecological model. Quantitative measures for mediators and recreational PA were then developed, and data from 301 women and girls were collected. Standard mediation analyses methods were then applied. Results: Program participation appeared to significantly increase PA levels. Statistically significant personal mediators were body issues, preferring competitions, and clothing. Social mediators were support from sports council, community leaders, friends, and church. Environmental mediators were travel time and access to balls, bibs, and umpires. Conclusion: A comprehensive community-level program addressing key participation barriers can increase recreational PA among women and girls in Tonga. Triangulating these results with mediation analyses of variables on the causal pathway can strengthen our understanding of causation and inform funding prioritization for critical program components in similar contexts.