Born in New York City in 1938, Dr. O'Connell received a Doctor of Medicine from Cornell University Medical College (1963), during which he was awarded a fellowship to Oxford University Medical School studying blood-clotting mechanisms with the late Professor Robert Gwyn Macfarlane, CBE. FRS.
He subsequently completed a surgical internship and residency in psychiatry at St. Vincent's Hospital and Medical Center of New York. Dr. O'Connell took a temporary leave while in residency to serve as a captain in the United States Army Medical Corps and Chief of Neuropsychiatry at Ireland Army Hospital in Fort Knox.
Following his service, he returned to St. Vincent's completing a fellowship in psychopharmacology before joining the medical staff as Chief of Psychiatry Inpatient Service and later as vice chairman and clinical director under Joseph T. English, M.D.
In 1996 Dr. O'Connell was appointed Provost and Dean of the School of Medicine at New York Medical College, stepping down in 2012. He continued as a professor of psychiatry and the behavioral sciences until 1995. He is currently the Vice Chairman for Research at New York Medical College.