Cushman was elected as Democratic-Republican from Massachusetts to the Sixteenth Congress (March 4, 1819-March 3, 1821). When the State of Maine was admitted into the Union, he was also elected as a Democratic-Republican member to the Seventeenth Congress, and reelected as a Adams-Clay Republican to the Eighteenth Congress (March 4, 1821-March 3, 1825). He died in Augusta, Maine on January 27, 1834. He was interred in a tomb on the State grounds in Augusta.