Leo Margolis, OCFRSC (December 18, 1927 – January 13, 1997) was a Canadian parasitologist. He was a pioneer in the use of parasites for identification of Pacific Ocean fish stocks. His discoveries became a crucial point in negotiations over pacific salmonfisheries, as it could now be determined where each individual fish spawned, in the rivers of Canada or the United States.
Born in Montreal, Quebec, he received a B.Sc. in 1948, a M.Sc. in 1950, and a Ph.D in 1952 from McGill University. He joined the Pacific Biological Station in Nanaimo, British Columbia, where was a government scientist, advisor, and diplomatic representative. He became Head of the Fish Health and Parasitology Section of the Station in 1967 and was appointed Senior Scientist in 1990. He suffered a heart attack in 1997 while walking home from work and died several days later, at the age of 69, after being airlifted to a Vancouver hospital.