Objective: Researchers from underrepresented groups leave research positions at a disproportionate rate. We aim to identify factors associated with self-efficacy in career advancement and career commitment among underrepresented post-doctoral fellows and early-career faculty. Methods: Building Up is a cluster-randomized trial with 25 academic health institutions. In September-October 2020, 219 Building Up participants completed the pre-intervention assessment, which included questions on demographics, science identity, mentoring, selfefficacy in career advancement (i.e., advancement is open to me, confidence in career progression, confidence in overcoming professional barriers), and career commitment (i.e., intent to continue research training or studying in a field related to biomedical sciences). Using logistic and multinomial logistic regression, we identified characteristics independently associated with self-efficacy in career advancement and career commitment. Results: The cohort is 80% female, 33% non-Hispanic/Latinx Black, and 34% Hispanic/Latinx. Having mentors that address diversity was significantly associated with the belief that advancement is open to them (OR = 1.7). Higher science identity (OR = 4.0) and having mentors that foster independence (OR = 1.8) were significantly associated with confidence in career progression. Higher science identity was also significantly associated with confidence in overcoming professional barriers (OR = 2.3) and intent to continue studying in a field related to biomedical sciences (OR = 3.3). Higher age (OR = 2.3) and higher science identity (OR = 4.2) were significantly associated with intent to continue research training. Discussion: Science identity and mentoring play key roles in self-efficacy in career advancement and career commitment. These factors may contribute to retention of underrepresented early-career biomedical researchers.