Louis J. Ignarro (born May 31, 1941) is an American pharmacologist. He was co recipient of the 1998 Nobel Prize in Physiology or Medicine with Robert F. Furchgott and Ferid Murad for demonstrating the signaling properties of nitric oxide.

He is currently professor of pharmacology at the UCLA School of Medicine's department of molecular and medical pharmacology in Los Angeles, which he joined in 1985. Before relocating to California, he was a professor of pharmacology at Tulane University School of Medicine, New Orleans, for 12 years. Ignarro has also previously worked as a staff scientist, research department, for the pharmaceutical division of CIBA-GEIGY Corporation in New York.

Ignarro has published numerous articles on his research. He received the Basic Research Prize of the American Heart Association in 1998, in recognition of his outstanding contributions to the advancement of cardiovascular science. That same year, he was inducted into the National Academy of Sciences and the following year, into the American Academy of Arts and Sciences.

He is the founder of the Nitric Oxide Society, and founder and editor-in-chief of Nitric Oxide Biology and Chemistry.^[1] Ignarro holds a B.S. in pharmacy, Columbia University, 1962, and a Ph.D. in pharmacology, University of Minnesota, School of Medicine, 1966. He also received a postdoctoral fellowship in chemical pharmacology from National Institutes of Health in 1968. He is a member of the scientific committee of Nicox, a French pharmaceutical company, a member of the Board of Directors of Antibe Therapeutics^[2], a Canadian drug discovery company, a member of the Board of Directors of Operation USA, a non-profit organization, and a member of the Nutritional Advisory Board for Herbalife, a for-profit nutrition and weight-loss company.