Henry Winter Davis (August 16, 1817 – December 30, 1865) was a United States Representative from the 4th and 3rd congressional districts of Maryland, well known as one of the Radical Republicans during the Civil War. He was the driving force behind the abolition of slavery in Maryland in 1864, and it was largely because of him that Maryland did not secede. He was an author and primary sponsor of the failed Wade–Davis Bill of 1864, which President Abraham Lincoln vetoed for going beyond his plans for Reconstruction.

Henry Winter Davis was born in Annapolis, Maryland on August 16, 1817. His father, the Reverend Henry Lyon Davis (1775–1836), was a prominent Maryland Episcopal clergyman, and was for some years president of St John's College at Annapolis. The son graduated at Kenyon College at Gambier, Ohio in 1837, and from the law department of the University of Virginia in 1841, and began the practice of law in Alexandria, Virginia, but in 1850 removed to Baltimore, Maryland, where he won a high position at the bar.

He wrote an elaborate political work entitled The War of Ormuzd and Ahriman in the Nineteenth Century (1853), in which he described the American Republic and the Russian Empire as the ultimate opponents in the struggles of humanity; it also dismissed the Southern contention that slavery was a divine institution.

Early becoming imbued with strong anti-slavery views, though by inheritance he was himself a slaveholder. He began political life as a Whig. After the Whig Party disintegrated, he became a Know Nothing, and served as a member of the Know Nothing–influenced American Party in the House of Representatives from 1855 to 1861. In 1856 he told Congress the unamerican Irish Catholic immigrants were to blame for the election of Democrat James Buchanan, stating:

The recent election has developed in an aggravated form every evil against which the American party protested. Foreign allies have decided the government of the country -- men naturalized in thousands on the eve of the election. Again in the fierce struggle for supremacy, men have forgotten the ban which the Republic puts on the intrusion of religious influence on the political arena. These influences have brought vast multitudes of foreign-born citizens to the polls, ignorant of American interests, without American feelings, influenced by foreign sympathies, to vote on American affairs; and those votes have, in point of fact, accomplished the present result.

In the contest over the speakership at the opening of the 36th United States Congress in 1859 he voted with the Republicans, incurring a vote of censure from the Maryland Legislature, which called upon him to resign.

In the 1860 presidential election, not yet ready to become a Republican, he declined to be a candidate for the Republican nomination for Vice President of the United States, instead supported the Constitutional Union ticket of John Bell and Edward Everett. Defeated that year for reelection to Congress, in the winter of 1860 and 1861―between the secession of some Southern states and the beginning of the Civil War with the assault on Fort Sumter―Davis was involved in compromise measures.

After Abraham Lincoln was elected and the Civil War began, Davis emerged as the leader of Maryland's Unconditional Unionists. He was re-elected in 1862 to the U.S. House of Representatives and quickly aligned himself with the Radical Republicans.