Background <p>The World Health Organisation estimates that worldwide six percent of women aged 15–49 have experienced non-partner sexual violence (NPSV) in their lifetimes. A similar prevalence is found in sub-Saharan Africa. This form of violence is comparatively under-researched, leading to a dearth of knowledge around potential risk factors for male perpetration of NPSV.</p> Methods <p>We sought to explore key risk factors for perpetration of non-partner rape, verbal and physical sexual harassment in young Tanzanian men by conducting a cross-sectional survey of 1002 young men aged 18 to 24 living in Mwanza, Tanzania between June 2021 and March 2022. We conducted unadjusted logistic regression for bivariate associations between all three forms of NPSV and risk factors at the sociodemographic, behavioural, and mental health and substance misuse level. The risk factors independently associated with the outcomes were included in three separate multivariable logistic regression models. We then used dominance analysis to determine which factors had the strongest association with all three forms of NPSV perpetration.</p> Results <p>Among the young men in our sample, 9% reported having perpetrated non-partner rape (<i>n</i> = 86), 19% having physically harassed a woman (<i>n</i> = 188) and 33% having verbally harassed a woman (<i>n</i> = 330). After adjustment for the other risk factors in the model, pornography consumption, having multiple sexual partners, gambling, and depressive symptoms remained significantly associated with more than one form of NPSV.</p> Conclusions <p>The widespread nature of sexual harassment and rape perpetration among young men in our study and the associated risk factors, which are all tied to notions of masculinity encouraging domination, promiscuity, and risky health behaviours, call for harmful gender norms to be addressed to reduce the incidence of NPSV.</p>