Tillman was elected as a Democrat to the Sixty-fourth and to the six succeeding Congresses (March 4, 1915-March 3, 1929). He was one of the managers appointed by the House of Representatives in 1926 to conduct the impeachment proceedings against George W. English, judge of the United States District Court for the Eastern District of Illinois. He did not seek renomination in 1928. He died in Fayetteville, Arkansas, March 9, 1929. He was interred in Evergreen Cemetery.