Magnuson was elected in 1952 as a Democrat to the Eighty-third Congress and was re-elected four times, serving from January 1953 until January 1963. Magnuson was named to the Committee on Merchant Marines and Fisheries in 1955. During his time in Congress he served on the Appropriations Committee subcommittee on Department of State, Justice and Judiciary, and the Department of the Interior. He also served on the Public Works Committee with oversight over the United States Army Corps of Engineers, Bureau of Reclamation, and the Atomic Energy Commission.