Background: The retention of traditionally underserved students remains a pressing problem across graduate engineering programs. Disciplinary differences in graduate engineering identity provide a lens to investigate students' experiences and can pinpoint potential opportunity structures that support or hinder progress based on social and personal identities. Purpose: This study investigates the impact of discipline, gender, race/ethnicity, advisor relationship, and years in a program on graduate engineering identity variability. Methods: Cross-sectional survey data from a national sample of doctoral engineering students were analyzed with multilevel modeling. Multilevel modeling measured the differences at the individual and discipline levels for graduate engineering identity and the domains of engineer, researcher, and scientist. Independent variables included were gender, advisor relationship score, race/ethnicity, and years in a program. Results: The engineer identity sub-construct of recognition significantly varied among engineering disciplines. Traditionally underserved students (i.e., Women and minoritized racial/ethnic groups) expressed lower engineering recognition levels, with this relationship varying based on discipline. Overall, our model explained 30% of the variation in engineering recognition among disciplines. Conclusions: The disciplinary variation in graduate engineering identity combined with the significance of gender and race/ethnicity indicates traditionally underserved students do not experience equivalent opportunity structures compared with their well-represented peers. Modifying traditional opportunity structures to serve students better may provide the needed changes to engage and retain traditionally underserved populations.