 He was elected to the 68th United States Congress in 1923 to fill the vacancy caused by the death of Luther W. Mott and served from November 6, 1923 until his death in office, having been re-elected to the 69th and 70th United States Congresses.Thaddeus Sweet was the first sitting member of Congress to die in an airplane accident.Shortly after breakfast on May 1, 1928, he and the pilot Lt. Bushrod Hoppin, U.S. Army, took off in a new Army observation plane, Curtiss O-1B Falcon, serial number "27-279", assigned at Middletown Air Depot, Pennsylvania, from Bolling Field to fly to Oswego, New York, where he was to make a speech.