After graduating, Hemphill practiced law in Chester. He was an unsuccessful candidate for the state legislature in 1874. He served as member of the South Carolina House of Representatives from 1876 to 1882. He was elected as a Democrat to the Forty-eighth and to the four succeeding Congresses (March 4, 1883 – March 3, 1893). He served as chairman of the committee on the District of Columbia (Fiftieth and Fifty-second Congresses). He was an unsuccessful candidate for reelection in 1892 to the Fifty-third Congress. He resumed the practice of law in Washington, D.C. at the Washington Loan and Trust Building, while retaining his residence in South Carolina. He was an unsuccessful candidate for election as United States Senator from South Carolina in 1902.[1][4] He wrote a number of books, including Why The Solid South.[2]