 Two years later, he served as a member of the Pennsylvania State House of Representatives in 1898 and 1900.Cassel was elected as a Republican to the Fifty-seventh US Congress to fill the vacancy caused by the death of Representative Marriott Brosius.He was reelected to the Fifty-eighth, Fifty-ninth, and Sixtieth Congresses, serving as Chairman of the United States House Committee on Accounts during the Fifty-ninth Congress.