1854–55 United States House of Representatives elections

States held the 1854–55 United States House of Representatives elections between August 4, 1854, and November 6, 1855, to elect the 234 members and five non-voting delegates of the United States House of Representatives. The Democratic Party remained the largest party but lost almost half its seats, while Know Nothings and the Anti-Nebraska movement made large gains. The Whig Party largely failed to capitalize on the weakness of its major rival, signaling the collapse of the Second Party System.

Controversy surrounding the Kansas-Nebraska Act and nativist opposition to Catholic immigration dominated the 1854 United States elections. Popular outrage against the Nebraska law produced new political parties in Indiana, Ohio, Michigan, and Wisconsin that included most former Whigs, Free Soilers, and Anti-Nebraska Democrats. As many as one in four Northern Democrats abandoned their party, while Democrats suffered a net loss of 70 seats in the free states. Northern Whigs hoped to benefit from Democratic misfortunes, but were weighed down by their own internal divisions and the rise of the Know Nothing movement in the Northeastern United States. Know Nothings swept Massachusetts and made gains in New York and Pennsylvania, where Whig candidates in some districts formed alliances with local lodges. In Iowa, Illinois, and Vermont, Whigs felt compelled to appeal to Free Soilers to shore up their sagging margins. The willingness of Northern Whigs to cooperate with Free Soilers and abolitionists, combined with the magnitude of Whig losses in the Northeast, led Southern Whigs to defect en masse to the Know Nothings in elections held in 1855.

No party controlled a majority in the lower chamber when the 34th United States Congress met in December 1855, leading to a protracted struggle to organize the House. Different groupings of Whigs, Know Nothings, and Anti–Nebraska men controlled between 105 and 117 seats in the House of Representatives, short of the 118 votes needed to elect a speaker. After two months of deadlock, the rule requiring a majority to elect the speaker was suspended; Massachusetts representative Nathaniel P. Banks was elected by a coalition of free state members on the 133rd ballot. The coalition supporting Banks became the base for the Republican Party, which emerged as the main opposition to the Democrats during the 1856 United States elections.