Horatio Seymour (sē´môr, sē´mər), 1810–86, American politician, b. Pompey Hill, N.Y. He studied law at Utica, N.Y. and was admitted to the bar in 1832. A Democrat, he was military secretary to Gov. William L. Marcy (1833–39), was thrice elected to the New York state assembly (1841, 1844, 1845), and was chosen mayor of Utica in 1842. Elected governor in 1852, he was criticized for vetoing a prohibition bill and was defeated for reelection. Again elected (1862) governor, Seymour declared the Emancipation Proclamation unconstitutional, opposed federal conscription as an unwarranted invasion of states' rights (but vigorously promoted voluntary enlistments), and denounced the military arrest of Clement L. Vallandigham. His speech in New York City on the occasion of the draft riots (July, 1863) played into Republican hands and was a factor in his defeat (1864). He was the Democratic presidential candidate in 1868, and after his defeat by Ulysses S. Grant he assumed the role of elder statesman in his party.
See biography by S. Mitchell (1938, repr. 1970).