As the author of the Wilmot Proviso, David Wilmot (1814-1868), U.S. congressman, initiated the legislative effort to prohibit the expansion of slavery.
David Wilmot, the son of a prosperous merchant, was born in Bethany, Pa., on Jan. 20, 1814. He studied law, was admitted to the Pennsylvania bar in 1834, and opened a practice in Towanda, Pa., in 1836, shortly after his marriage. He became more interested in politics than in law. An active and ardent Jacksonian Democrat, noted for his extemporaneous oratorical skills, he played a major role in Pennsylvania's Democratic state convention in 1844 and won a congressional seat, which he held from 1845 to 1851.
Initially Wilmot loyally supported the measures of James K. Polk's administration, although he had strongly supported Polk's opponent, Martin Van Buren, in the 1844 Democratic National Convention. During the Mexican War, however, Wilmot and other Northern and Western Democrats became convinced that Polk's policies would give the Southern wing of the party permanent dominance. Proslavery political power had already been enhanced by the acquisition of Texas. Northern and Western Democrats feared its further growth through the potential acquisition of more slave territory from Mexico.
Thus, when Polk requested funds to conduct peace negotiations with Mexico in 1846, Wilmot attached to the appropriations bill his famous proviso that slavery be absolutely prohibited in any territory acquired through those negotiations. Wilmot's measure passed in the House of Representatives but was blocked in the Senate. The Southern congressional bloc, led by John C. Calhoun, immediately countered with resolutions stating that property rights ("property" including slaves) were guaranteed by the Constitution and had to be fully protected in all Federal territories.
The principles stated in this debate permanently polarized proslavery and antislavery factions. Attempts at reconciliation—in the Compromise of 1850 and the 1854 Kansas-Nebraska Act—only temporarily averted the confrontation. Ultimately the controversy over slavery in the territories split the nation's political parties asunder. When Abraham Lincoln, pledging unalterable opposition to any future extension of slavery in the United States, was elected in 1860, the slave states refused to accept their political defeat, and the stage was set for the Civil War.
Wilmot made no further notable political contributions. He held a judgeship from 1851 until 1861 and served in the U.S. Senate from 1861 to 1863. Lincoln appointed him to a Federal judgeship which he retained until his death on March 16, 1868, in Towanda.
Charles B. Going, David Wilmot: Free-Soiler (1924; new ed. 1966), is a thorough and competent biography. A lengthy discussion of the Wilmot Proviso is in Allen Nevins, Ordeal of the Union (2 vols., 1947).