Horatio Seymour, the son of a banker, was born in Pompey Hill, New York, on 31st May, 1810. Trained as a lawyer, he served as military secretary to the New York governor, William M. Marcy from 1833 to 1839.
In 1841 Seymour was elected to the lower house of the New York Legislature (1842-46). Her served as Speaker (1845-47) and in 1852 was elected as governor of New York but was defeated two years later, mainly because of his refusal to support prohibition.
On the outbreak of the American Civil War Seymour initially supported Abraham Lincoln but urged a peaceful settlement of the conflict. When he criticised Lincoln's excessive use of executive power, he was accused of being sympathetic to the Southern cause.
In 1868 Seymour was nominated as the Democratic candidate to run against Ulysses S. Grant. During the campaign, Thomas Nast, produced several cartoons for Harper's Weekly attacking his campaign. One of these drawings shows Seymour joining hands with the Irish vote and the Confederate vote to prevent the Negro from reaching the ballot box. Seymour fought a good campaign and only lost by 300,000 votes.