Born in Washington County, Kentucky, Hays read law in 1845. He entered private practice of law in Springfield, Kentucky from 1845 to 1851. He was a county judge in Washington County from 1851 to 1859. Hays resumed private practice in Springfield from 1859 to 1860. He was a member of the Kentucky House of Representatives in 1861. He was in the United States Army as a colonel from 1861 to 1866. Upon the resignation of its first commander, Hays became commanding officer of the 10th Kentucky Infantry. During the Battle of Chickamauga, Hays assumed command of the II Corps and eventually command of the 2nd division. He rose to the rank of general officer. Following the American Civil War, he was State inspector general of Kentucky from 1865 to 1866. He was an oil and gas entrepreneur in Springfield from 1866 to 1867 and in private practice there from 1867 to 1879.