Thaddeus Stevens , (born April 4, 1792, Danville, Vermont, U.S.—died August 11, 1868, Washington, D.C.), U.S. Radical Republican congressional leader during Reconstruction (1865–77) who battled for freedmen’s rights and insisted on stern requirements for readmission of Southern states into the Union after the Civil War (1861–65).

Admitted to the Maryland bar, he moved to Pennsylvania to practice law in 1816. Having witnessed the oppressive slave system at close range, he early developed a fierce hatred of bondage and defended numbers of fugitives without fee. An anti-Masonic member of the state legislature (1833–41), he proved himself a friend of banks, internal improvements, and public schools and a foe of Freemasons, Jacksonian Democrats, and slaveholders. Serving as a Whig in the U.S. House of Representatives (1849–53), he advocated tariff increases and opposed the fugitive slave provision of the Compromise of 1850.

In the middle of the decade he joined the newly formed Republican Party, which opposed extension of slavery into the western territories; again he was elected to Congress (1859–68), where he became, in the words of a fellow member, the “natural leader, who assumed his place by common consent.” He exerted this leadership by means of his sarcastic eloquence, his parliamentary skills, and his privileges as chairman of the Ways and Means Committee and later of the Appropriations Committee.

After the war Stevens emerged as one of the most militant of the Radical Republicans, consistently striving for justice for the black masses. Alert to the return to power of traditional white Southern leadership, he argued that the seceded states were in the condition of “conquered provinces” to which restraints of the Constitution did not apply.

When Congress met in December 1865, Stevens took the lead in excluding the traditional senators and representatives from the South. As a member of the joint Committee on Reconstruction, he played an important part in the preparation of the Fourteenth (due process)