Key Social Norms Take-aways The study shows that shifting men’s attitudes around gender norms is possible through peer-led interventions, but changing behaviors tied to power, masculinity, and violence demands deeper, sustained engagement. Effective interventions must focus not only on individual beliefs but also on the community and relational dynamics that reinforce harmful practices. Objectives: This study evaluated whether combining a microfinance and peer health leadership intervention within male social networks (camps) in Dar es Salaam, Tanzania, could reduce sexually transmitted infections (STIs) and intimate partner violence (IPV) perpetration. Specifically, it examined whether addressing both economic barriers and social norms around masculinity and power could shift men’s behaviors related to HIV risk, violence, and gender attitudes. Methods: A cluster-randomized controlled trial was conducted across 60 male camp-based social networks (30 intervention, 30 control), enrolling 1,258 men. Intervention camps received a two-year program combining business development loans and microfinance training with peer health leadership education focused on gender-based violence, HIV prevention, and condom use. Data were collected at baseline and after 30 months, including biological testing for STIs, self-reported IPV perpetration, HIV testing history, and attitudes toward gender roles, measured using the Gender Equitable Men (GEM) scale. Intervention Details: The intervention had two parts: (1) microfinance training and small business loans with group savings and escalating access, and (2) peer health leadership, where about 20% of camp members were trained to engage peers in conversations about reducing HIV risk, IPV, and promoting gender equity, with booster sessions every six months. Results: At 30 months, no significant differences were observed between intervention and control groups regarding STI prevalence, IPV perpetration, or sexual risk behaviors. However, the intervention group reported a higher rate of past-year HIV testing (aRR 1.13, 95% CI 1.005–1.28) and significantly lower levels of inequitable gender norm attitudes (adjusted effect −0.11, 95% CI −0.21 to −0.003). While the intervention partially shifted attitudes and testing behaviors, it did not lead to measurable reductions in violence or STI outcomes during the study period. Conclusions: This combined intervention highlights the challenge of translating changes in gender attitudes into changes in deeply entrenched behaviors like violence and sexual health practices. Addressing structural barriers and gender norms together holds promise, but meaningful reductions in IPV and STI risk may require longer or more intensive interventions, or strategies tailored specifically to behavioral change.