Male perpetration of intimate partner violence (IPV) against women in Tanzania is widespread. Theory and empirical evidence suggest peer networks may play an important role in shaping IPV perpetration, although research on this topic in sub-Saharan Africa is limited. Grounded in social learning theory, social influence theory, and the theory of gender and power, the purpose of this study was to examine whether and how peer networks influence men's perpetration of IPV in Dar es Salaam, Tanzania. We conducted in-depth interviews (n = 40) with a sub-sample of 20 men enrolled in the control condition of an ongoing cluster-randomised controlled trial. We purposively sampled participants who previously reported perpetrating physical IPV. To analyse the data, we generated narrative summaries and conducted thematic and interpretative coding. We saw no evidence that men self-selected into peer networks with certain values or behaviours. Rather, men described several mechanisms through which their peers influenced the perpetration of IPV, including: (1) the internalisation of peer network norms, (2) pressure to conform to peer network norms and (3) the direct involvement of peers in shaping couple power dynamics. Our findings suggest that peer networks influence men's perpetration of IPV and should be targeted in future programmes and interventions.