Identifying as a “science person” is predictive of science success, but the mechanisms involved are not well-understood. We hypothesized that science identity predicts success because it fosters a sense of belonging in science classrooms. Thus, science identity should be particularly important for first-generation and racial-minority students, who may harbor doubts about belonging in science. Two field studies in college Introductory Biology classes (Ns = 368, 639) supported these hypotheses. A strong science identity predicted higher grades, particularly for minority students. Also consistent with hypotheses, Study 2 found that self-reported belonging in college mediated the relationship between science identity and performance. Furthermore, a social belonging manipulation eliminated the relationship between science identity and performance among minority students. These results support the idea that a strong science identity is particularly beneficial for minority students because it bolsters belonging in science courses. Practical and theoretical implications are discussed.