John R. Thornton (August 25, 1846 - December 28, 1917) was a United States Senator from Louisiana. Born on Notoway plantation (near Bayou Goula in Iberville Parish), he moved with his parents to Rapides Parish in 1853. He attended Parker Seminary (Pineville), the McGruder Institute (Baton Rouge) and the Louisiana Seminary (afterwards the Louisiana State University) at Pineville until 1863. He enlisted in the Confederate Army and served until the close of the Civil War in Company B, Second Louisiana Cavalry. He engaged in agricultural pursuits until 1877, studied law, was admitted to the bar in 1877 and commenced practice in Rapides Parish. He was judge of Rapides Parish from 1878 to 1880 and a delegate to the State constitutional convention in 1898. From 1904 to 1910 he was a member of the board of supervisors of the State university.
Thornton was appointed as a Democrat to the U.S. Senate on August 27, 1910, and wassubsequently elected to fill the vacancy caused by the death of Samuel D. McEnery, serving from December 7, 1910, to March 3, 1915; he was not a candidate for reelection to the Senate. While in the Senate he was chairman of the Committee on Fisheries (Sixty-third Congress). He was appointed by President Woodrow Wilson a member of the Board of Ordnance and Fortification and served from 1915 to 1917, and resumed the practice of law in Alexandria, Louisiana; he died there in 1917. Interment was in Rapides Cemetery, Pineville.