INTRODUCTION: Women's groups have emerged as an essential platform for implementing violence prevention interventions across diverse settings because they can serve as a powerful catalyst for promoting gender equality, empowering women, and providing a safe space for them. Given the limited empirical evidence on the impact of women's informal group participation on male-perpetrated intimate partner violence, this longitudinal study examines how such participation influences women's experiences of physical, emotional, sexual, and economic IPV in Mwanza, Tanzania. METHODS: Data from four waves of the MAISHA study, which followed up the control groups (n = 1122) of the two MAISHA trials, were analysed. Women aged 18-70 who had been in a relationship within the last 12 months were included. Using mixed effects logistic regression models, we examined the association between women's active participation in religious, ethnic, microcredit, street and support groups and community meetings, with four types of IPV, adjusting for cohabitation status, age and enrolment in previous MAISHA trials. Participants' unique identification number was used as a random effect variable, and dummies for each survey round were used to account for time. RESULTS: The prevalence of religious, ethnic, microcredit, support and street groups, and community meeting participation at baseline were 41.8%, 17.5%, 41.1%, 20.1%, 42.9%, and 20.1%, respectively. Adjusted multivariable models showed that participants who engaged in community meetings reported lower odds of experiencing economic IPV (AOR = 0.68, CI: 0.56-0.82) and higher odds of experiencing emotional IPV (AOR = 1.21, CI: 1.00-1.46). Further, active participants of support groups reported lower odds of experiencing both economic (AOR = 0.77, CI: 0.60-0.99) and sexual IPV (AOR = 0.72, CI: 0.58-0.90). Participants in ethnic groups also reported lower odds of economic IPV (AOR = 0.79, CI: 0.62-1.00). No predictor was associated with physical IPV. CONCLUSION: This study underscores the potential of informal community group participation to mitigate sexual and economic IPV among women in Mwanza, Tanzania, while also indicating a possible increase in the risk of emotional IPV. It emphasises the necessity for tailored, context-sensitive, and gender-transformative interventions to address power imbalances and restrictive norms effectively. Future research should delve into nuanced measures of group participation, including attendance, meeting frequency and duration, participants' influence within groups, the strength of social ties, and their implications for IPV experiences.