Born in Darien, Georgia in 1849, Thomas moved to Michigan soon after the Civil War, attending private schools and then the University of Michigan, earning a law degree in 1871. In that same year he emigrated to Denver, Colorado and began a legal practice. From 1873-1889 Thomas was a junior member of the firm of Patterson Thomas, and during that period he also served as City Attorney of Denver from 1875-1876. In 1890 he established the firm of Thomas, Bryant Lee; he also became a prominent member of the Democrat party in Colorado, and an ardent supporter of William Jennings Bryan and the free silver movement. In 1898 Thomas was nominated by the Democrats for Governor, and his candidacy was supported by the Silver Republicans and Populists of Colorado. He won a landslide election against Henry R. Wolcott, and served one term from 1899-1901. After his stint as governor, Thomas returned to his private legal practice, but in 1913 he was appointed to the U.S. Senate to fill the unexpired term of Charles J. Hughes. Thomas won reelection in 1915, and served until 1921 in the Senate. During his tenure in the Senate he was closely associated with William E. Borah and others in opposition to Woodrow Wilson's advocacy of the League of Nations; he also served on a number of Senate Committees, including Finance and Foreign Relations. He was also instrumental in establishing the U.S. Air Force as a separate branch of the military rather than under the control of the Army Signal Corps. In 1920 Thomas was defeated by Republican Sam Nicholson, and he then spent the next 8 years in Washington D.C. as an attorney working mainly for oil and mining. Thomas devoted the final years of his life at attempts to revive bimetallism in the United States. In 1928 Thomas retired to Denver, and died there in 1934.