On March 6, 1892, Clements was appointed by President Harrison to the Interstate Commerce Commission, filling the unexpired term of Commissioner Walter L. Bragg of Alabama, who had died. After being confirmed by the Senate, Clements was sworn in on March 17, 1892. On December 12, 1910, with the resignation of longtime Commission chair Martin A. Knapp, he became acting chairman of the Committee, and in 1911 became chairman of the Commission for a one-year term. In addition to being appointed by President Harrison, he was reappointed by Presidents Grover Cleveland, William McKinley, Theodore Roosevelt, and Woodrow Wilson, and served as a commissioner until his death in Washington, D.C., June 18, 1917.