Olav Anton Thommessen (born 16 May 1946) is a Norwegian composer. He trained in the United States earning degrees from Westminster Choir College and Indiana University. He is currently professor of composition at the Norwegian Academy of Music, where he has taught since 1972. He won the Nordic Council Music Prize in 1990 for his composition "Gjennom Prisme" for cello, organ and orchestra. Thommessen's compositions include numerous symphonic works, chamber music pieces, and vocal music works. He has written several operas.