Harold attained Bachelor of Arts degree in 1955, graduating from St. John’s College. Some time later, in 1968, he received Bachelor of Science degree at Loyola University. In 1970, De Lisle obtained Master of Science degree, graduating from the University of Puerto Rico. He continued his studies and ten years later, in 1980, got his Doctor of Philosophy degree at Columbia Pacific University.
Harold also attended University of California in Los Angeles.
In 1979 Harold started to work as an assistant professor of biology at University of Pasadena, a post he held until 1989, when he was appointed a professor of biology at Moorpark College in Moorpark, California.
Harold De Lisle is a member of American Society of Ichthyologists and Herpetologists, Herpetologists' League and Society for the Study of Amphibians and Reptiles.