Despite calls to engage men in HIV and intimate partner violence (IPV) prevention efforts, effective approaches to reach and engage men in low-resource, high-HIV prevalence settings are limited. We identified and engaged social networks of mostly young men in a study designed to evaluate the efficacy of a combined microfinance and peer health leadership intervention to prevent HIV and IPV. We conducted a cluster-randomized trial among 60 social networks locally referred to as "camps" within Dar es Salaam, Tanzania. Camps were randomly assigned (1:1) to a microfinance and peer health leadership intervention or a control condition that received a brief delayed intervention after the study's conclusion. Allocation was not masked to participants or researchers. Behavioral assessments were conducted at baseline and 30-months post-intervention launch, with biological samples drawn at 30-months to test for sexually-transmitted infections (STIs). Primary outcomes included prevalence of STIs and past-year IPV perpetration. Secondary outcomes included STI sexual risk behaviors and past-year HIV testing. Proximal intervention targets included inequitable gender norm attitudes and hope. A modified Poisson regression approach was used to estimate intention-to-treat intervention effects on outcomes assessed at the 30-month follow-up. We enrolled 1,258 men within 60 camps. Of these men, 1,029 (81.8%) completed the 30-month follow-up. There were no differences by condition in STI prevalence, IPV perpetration, or sexual risk behaviors at the 30-month follow-up. Intervention participants reported greater levels of past-year HIV testing, controlling for baseline testing (aRR 1.13 95% CI 1.005-1.28). They also reported significantly lower levels of inequitable gender norm attitudes (adjusted effect -0.11, 95% CI -0.21-0.003). We successfully engaged and retained social networks of men in this multilevel intervention study. While we did not see an effect on the primary outcomes, our intervention successfully improved HIV testing and reduced inequitable gender norm attitudes.