We tested the long-term effects of a utility-value intervention administered in a gateway chemistry course, with the goal of promoting persistence and diversity in STEM. In a randomized controlled trial (N = 2,505), students wrote three essays about course content and its personal relevance or three control essays. The intervention significantly improved STEM persistence overall (74% vs. 70% were STEM majors 2.5 y later). Effects were larger for students from marginalized and underrepresented racial/ethnic groups, who were 14 percentage points more likely to persist in STEM fields in the intervention condition (69% vs. 55%). Mediation analysis suggests that the intervention promoted persistence for these students by bolstering their motivation to attain a STEM degree and by promoting engagement with course assignments. This theory-informed curricular intervention is a promising tool for educators committed to retaining students in STEM.