Youth who witness parental intimate partner violence are at increased risk for sexual violence. Existing data from a cluster RCT were used to determine the effectiveness of Green Dot bystander intervention to reduce sexual violence among high-school students who did and did not witness parental intimate partner violence. A secondary analysis was conducted in 2021 of extant data from a 5-year cluster RCT. A total of 26 high schools in Kentucky were randomized to intervention or control condition in 2010. A total of 15,863 surveys were analyzed from baseline, 30,014 from partial intervention implementation (Years 1 and 2), and 25,907 from full implementation (Years 3 and 4). The sample was stratified to include students who witnessed or did not witness parental intimate partner violence. The bystander intervention program was delivered in 2 stages. During partial implementation, a persuasive speech describing rates, risk factors, and bystander-based approaches to violence prevention was provided to most students in schools randomized to the intervention. During full implementation, an in-depth 5-hour skill-based bystander training was provided to popular opinion leaders among the students in intervention schools (10%-15%). The primary outcome was sexual assault measured as perpetration and victimization. Secondary outcomes included sexual harassment and stalking, measured as victimization and perpetration. During full implementation, among students who witnessed parental intimate partner violence, the intervention was associated with significant reductions in sexual assault perpetration (β= -0.21, p<0.01), sexual harassment perpetration (β= -0.29, p<0.001), sexual assault victimization (β= -0.25, p<0.01), and sexual harassment victimization (β= -0.45, p<0.001). For students who did not witness parental intimate partner violence, the intervention was only associated with reductions in sexual harassment (β= -0.19, p<0.001) and stalking (β= -0.09, p<0.01) victimization. As implemented in the parent RCT, the bystander training was more effective at reducing violent outcomes among those who witnessed parental intimate partner violence than in those who did not witness parental intimate partner violence. This study is registered at www. gov, under identifier NCT01878097.