Reed Smoot was elected to the United States Senate as Republican in 1902. His election sparked a bitter four-year battle in the Senate over whether he should be allowed to serve due to his position as a Mormon apostle and the Mormon Church's policy regarding plural marriage, among other concerns. During these four years, the Mormon Church was on trial as much as was Reed Smoot. Smoot was finally allowed to take his seat in the Senate on 20 February 1907. He was reelected in 1908, 1914, 1920, and 1926, and served from 4 March 1903 to 3 March 1933. Because of the Senate seniority system, Smoot served as chairman of the powerful Senate Finance Committee from 1923 to 1933, as well as on the Senate Appropriations Committee. Senator Smoot was recognized as an expert on government finance and public land issues. He was known for his discipline, hard work, integrity, and thorough preparation. His politics were conservative and pro-business. He is perhaps best known as the joint author of the famous if often criticized Smoot-Hawley Tariff Act.
Reed Smoot was active and prominent in the national Republican party. He served as a delegate to the Republican national conventions in 1908, 1912, 1916, 1920, and 1924, and was chairman of the Resolutions Committee at the 1928 Republican National Convention. He also served as chairman of the Republican Senatorial Campaign Committee. He became an accepted member of the inner club of the national Republican establishment and was an advisor to a number of Republican presidents. Smoot was acknowledged as the de facto leader of the Utah Republican party and had considerable influence over Utah state politics and politicians.