| Stephen Hanessian | |
| Birth Place: | Alexandria, Egypt |
| Occupation: | Chemist, academic |
Stephen Hanessian, OC, FRSC, (born April 25, 1935) is a chemist and professor of Canadian and United States citizenship born in Alexandria, Egypt. His research group at Université de Montréal is well known for developing synthetic methodologies, as well as natural product total synthesis. In addition, his group developed Chiron, a computer program used by organic chemists for synthetic planning.
He earned his Ph.D. at Ohio State University in 1960, under the direction of M. L. Wolfrom. He worked as a researcher for Parke-Davis & Co. in Ann Arbor, Michigan until 1968. In 1969 he joined Université de Montréal. Since 2000, he has also been an adjunct professor at University of California, Irvine.