Knox Martin was born in 1923 in Barranquilla, Colombia. He is the son of the aviator, painter, and poet William Knox Martin, the first man to fly over the Andes mountains. After serving in World War II, Knox Martin attended the Art Students League of New York on the G.I. Bill from 1946-1950, where he studied with Harry Sternberg, Vaclav Vytlacil, Will Barnet, and Morris Kantor.