Horatio Seymour (May 31, 1810 - February 12, 1886) was an American politician. He was Governor of New York State from 1853-1854 and from 1863-1864. He was the Democratic Party nominee for President of the United States in the U.S. presidential election, 1868, but lost the election to Republican Ulysses S. Grant.
Horatio Seymour was born in Pompey Hill, Onondaga County, New York, educated at Geneva Academy (later Hobart College) and at Middletown (Conn) Military Academy, studied law at Utica, and in 1832 was admitted to the bar. He served as mayor of Utica, New York from 1842 to 1843.
He served as Governor of New York from 1853 to 1854 and again from 1863 to 1864. As governor of New York in 1863 to 1864, he became a leading Northern opponent of President Abraham Lincoln's administration during the American Civil War. Seymour protested Lincoln's restriction of civil liberties during the Civil War, as well as the Emancipation Proclamation and the Union's military draft. He advocated the vigorous prosecution of the war, but protested against the extensive use of war powers by Lincoln.
In 1868 he was president of the Democratic National Convention which met in New York City, and received its presidential nomination. In the general election, he ran on the slogan: "This Is a White Man's Country: Let White Men Rule." He received 80 electoral votes against 214 for Grant.
After this he took no further part in political affairs.