Born in Hamilton County, Ohio, on February 3, 1846, Harmon graduated in 1866 from Denison University, Granville, Ohio. In 1869 he graduated from the Law School of Cincinnati College, was admitted to the bar, and entered into the practice of law. Harmon was elected judge of the common pleas court in 1876, but was unseated four months later after a State senate contest. Two years later, he was elected judge of the superior court of Cincinnati, reelected in 1883, and resigned in 1887 to resume the practice of law. He was appointed Attorney General of the United States by President Cleveland on June 8, 1895, and served until March 5, 1897. Harmon was also elected as Governor of Ohio in 1908, reelected twice, and made an unsuccessful bid for the Democratic nomination for President in 1912. He died on February 22, 1927, in Cincinnati, Ohio.