Importance: Despite the importance of clinician-scientists in propelling biomedical advances, the proportion of physicians engaged in both hypothesis-driven research and clinical care continues to decline. Recently, multiple institutions have developed programs that promote MD-only physicians pursuing careers in science, but few reports on the impact of these are available. Objective: To assess if a cohort-based training program for MD-only physician-scientists that includes didactic and experiential curricula favorably informs participants' scientific development. Design: The Chan Zuckerberg Biohub (CZB) Physician-Scientist Fellowship Program (PSFP) conducted a study from July 2020 to August 2022. Participants: 24 inaugural program participants at UCSF and Stanford University (median postgraduate year at program start, 5.5; 17 clinical specialties represented; 10 [42%] identified as female; 7 [29%] identified as underrepresented in medicine). Exposures: The CZB PSFP is a selective two-year career development program for MD-only physicians. Participants attended a two-week immersive training at the program outset, and subsequently, weekly curricular and scientific meetings throughout the program while conducting research. Main Outcomes and Measures: Primary outcome measurements included pre-, 1-month, and 12-month assessments of confidence in research skills, career skills, and self-identification as scientists. Program satisfaction and feedback related to program curriculum and community were collected at 1 month, 6 months, and 12 months. Results: After 12 months, 94% reported satisfaction with the program and participants demonstrated increased confidence in research skills (mean [SD] pre vs. post, 3.79 [0.59] vs. 5.09 [0.42], P<0.01), confidence in career skills (4.00 [0.52] vs. 5.20 [0.38] P<0.01), personal identification as a researcher (4.71 [1.41] vs. 6.00 [1.33], P<0.01), and sense of belonging to a community of scientists (3.53 [1.40] vs. 5.75 [1.41] P<0.001). Conclusion and Relevance: Participants demonstrated significant gains in confidence in core research and career skills as well as personal identification as scientists, demonstrating the efficacy of a longitudinal curriculum, peer support, and community building in fostering development as an investigator. The highly portable nature of this strategy may facilitate ready adoption and implementation at other institutions.