To address the persistent underrepresentation of women and racial and ethnic minorities in STEM, the current study utilized a quasi-experimental posttest waitlist control group approach to examine the effect of a 1-year virtual peer mentoring program on the academic, professional, and psychosocial outcomes of graduate mentors and undergraduate mentees enrolled in STEM degree programs at two historically black institutions. The findings demonstrated that mentors and mentees participating in the mentoring program experienced increased levels of community, STEM achievement, career self-efficacy, and intent to persist in STEM degrees and careers. Mentors experienced increased interest in science, engineering, and technology, and mentees experienced increased interest in science, engineering, and mathematics. The implications of the program, especially among women and racial and ethnic minorities enrolled in historically black institutions, are discussed, as well as suggestions for future study.