Gregory Leong, M.D. served as a faculty member of the Department of Psychiatry and Behavioral Sciences at the University of Southern California from 1982 to 1986 before returning to the Department in 2012. During the intervening years, he has been on the medical school faculties at the University of California, Los Angeles, University of Missouri, Ohio State University, and University of Washington. While at the University of Washington Dr. Leong was the Director of the Forensic Psychiatry Fellowship from 2008 to 2011.

Dr. Leong's academic interests have primarily revolved around forensic psychiatry. While at the University of California, Los Angeles, he participated in research projects involving schizophrenia, post-traumatic stress disorder, and smoking cessation.

On the national level, Dr. Leong has served on the Executive Council of the American Academy of Psychiatry and the Law from 1997 to 2000, the Council of Psychiatry and Law of the American Psychiatric Association from 2002 to 2007, and the Committee on Recertification in Forensic Psychiatry of the American Board of Psychiatry and Neurology from 2000 to 2003.

Besides authoring or co-authoring numerous scholarly publications in the professional literature, Dr. Leong served as an associate editor of the Newsletter of the American Academy of Psychiatry and the Law from 1992 to 1999 and an associate editor of the Journal of the American Academy of Psychiatry and the Law from 2004 to 2009. Dr. Leong has been on the editorial board of Behavioral Sciences and the Law since 2017. Dr. Leong received the Golden Apple (AAPL) Award from the American Academy of Psychiatry and the Law (AAPL) in 2019 (in recognition of having made significant contributions to the field of forensic psychiatry).