Free-Soil party, in U.S. history, political party that came into existence in 1847–48 chiefly because of rising opposition to the extension of slavery into any of the territories newly acquired from Mexico. The struggle in Congress over the Wilmot Proviso helped to consolidate the Free-Soil forces, which comprised those New York Democrats known as Barnburners, the antislavery Whigs, and members of the former Liberty party. These forces met in mass convention at Buffalo in Aug., 1848, where the party was formally organized and Martin Van Buren and Charles F. Adams (1807–86) were chosen as its candidates for president and vice president. The platform also declared for a homestead law, internal improvements, and a tariff for revenue only. The party polled nearly 300,000 votes and, by giving New York state to the Whigs, was a decisive factor in making Zachary Taylor president. The party elected one senator, Salmon P. Chase of Ohio, and 13 congressmen. The Compromise of 1850 supposedly settled the slavery issue, and the Barnburner element went back to its old allegiance. A few radical antislavery men kept the organization in existence and nominated John P. Hale for president in 1852; he received more than 150,000 votes. In 1854 the party was absorbed into the new Republican party.
See T. C. Smith, The Liberty and Free Soil Parties in the Northwest (1897, repr. 1969); E. Foner, Free Soil, Free Labor, Free Men (1970); J. G. Rayback, Free Soil: The Election of 1848 (1970); F. J. Blue, The Free Soilers (1973).