Dr. De Leon took his PhD from Columbia University in 1962; his dissertation was entitled "Some Relations between Avoidance Responding and Cardiac Responses in Humans." He conducted research on behavior modification in humans using conditioning and later became a prominent psychologist in the field of drug rehabilitation. He was responsible for conducting all of the early Phoenix House studies researching the mechanisms used in treatment. He wrote the textbook The Therapeutic Community.
In 2014, Columbia University held and event where Dr. DeLeon described his work.