Despite significant declines, adolescent birth rates in the USA are higher than other industrialized countries, with black and Hispanic youth disproportionately affected. This study assessed the efficacy of a single-session, entertainment-education sexual health video intervention for these populations. Using an individual-level randomized controlled trial, 1770 18- to 19-year-old black and Hispanic females were assigned to watch Plan A (n = 886) or a control video (n = 884) prior to a sexual reproductive health (SRH) visit. Participants self-reported data at baseline and 3 months post-baseline. Within an intent-to-treat framework, we estimated the average causal effect of assignment to Plan A on three confirmatory and five exploratory outcomes. We found that individuals assigned to Plan A had higher contraceptive knowledge, may be more likely to get sexually transmitted infection (STI) testing, and may have elevated HIV/STI risk perceptions 3 months post-video. Although we found no difference in long-acting reversible contraception (LARC) use nor frequency of condomless sex in the full sample, we did observe that first-time SRH visitors assigned to Plan A had a higher probability of using LARC than those in the control group. This study demonstrates that Plan A is a low-burden, inexpensive, and highly scalable video intervention for black and Hispanic adolescent females that has significant and borderline significant effects on protective sexual health behaviors and important antecedents. It adds to the evidence base of effective teen pregnancy prevention programs and the limited set of rigorous and causal studies investigating the effectiveness of entertainment-education interventions on sexual risk reduction. Registered in ClinicalTrials.gov (NCT03238313) on August 3, 2017.