Though contemporary evidence suggests that upwards of one-in-nine UK male university students engage in sexually violent behaviors (Hales and Gannon in Sexual Abuse 34:744–770, 2022), few evidence-based primary prevention strategies have been developed to prevent their perpetration. To help contribute to this evidence gap, this study evaluated the short and longer-term effectiveness of a novel psychoeducation-based online self-help intervention for university male sexual aggression called The Pathways Programme. Designed around current empirical understanding of university-based sexual harm in the UK, the program contains six modules that correspond with known risk factors for perpetration. Data were collected as part of a randomized control trial from 254 self-identified heterosexual male students enrolled at a UK university who reported a proclivity towards sexual aggression. Results showed that participants who took part in the program displayed moderate reductions in their self-perceived likelihood of sexual aggression (our primary treatment target) across testing points, as well as reductions in their self-reported levels of hostility towards women, rape myth acceptance, and problematic sexual fantasies (our secondary treatment targets). Control participants also displayed reductions in some domains over time, albeit to a lesser degree. Additional analyses probed the factors associated with participant drop-out, clinical and reliable change, and user feedback. Overall, our study provides preliminary evidence for the efficacy of The Pathways Programme at reducing UK university males’ risk of sexual aggression; however, we caution readers that more robust evaluation is necessary to support intervention rollout. We discuss our findings alongside the limitations of our study and provide suggestions for future research.