Amadon was born in Milwaukee, Wisconsin to Arthur and Mary Amadon. He received a BS from Hobart College in 1934 and a Ph.D. from Cornell University in 1947. In 1937 he joined the American Museum of Natural History in New York City and was Chairman of the Department of Ornithology there from 1957 until 1973. In 1940, he married Octavia Gardella and had two daughters: Susan and Emily.
Amadon was a member of the American Association for the Advancement of Science, president of the American Ornithologists' Union from 1964 to 1966 and Linnaean Society. He joined The Explorers Club in 1959. His books included Eagles, Hawks and Falcons of the World (1968) with Leslie H. Brown, and Curassows and Related Bird (1973) with Jean Delacour. He died on January 12, 2003, in Tenafly, New Jersey.