1864–65 United States House of Representatives elections

The 1864–65 United States House of Representatives elections were held between June 5, 1864, and November 7, 1865, to elect the 192 members and nine non-voting delegates of the House of Representatives. The National Union Party expanded their existing majority against the backdrop of the American Civil War.

Candidates listed as Republicans and Unionists won 99 seats in congressional elections held in 1862 and 1863; three Union Democrats and the lone Unconditional Union Democrat from Kentucky subsequently crossed the floor to give the Republican-Union coalition a narrow majority during the 38th United States Congress. The wartime coalition of Republicans, War Democrats, and border state unionists became the base for the National Union Party that held its national convention at Baltimore on June 7, 1864. Leading Unionists were pessimistic about their party's prospects during the summer of 1864, but the fall of Atlanta led to a dramatic reversal of fortunes ahead of the fall elections. The Union Party won a "sweeping victory" at the polls, carrying all but three states in the concurrent presidential election.

Unionists significantly improved their showing compared to the last elections, contributing three-quarters of the members of the 39th United States Congress. A majority of the members elected from Indiana and all but two from Ohio were Unionists. In Kentucky, Missouri, and Tennessee, the elections were contested by Radical and Conservative Unionist factions, resulting in 15 Radical or Unconditional Unionists, 9 Conservatives, and 1 Independent Unionist elected to the 39th United States Congress.

Following the Confederate surrender, the former states of the Confederacy held congressional elections in 1865 and 1866, but only the members from Tennessee were seated by the House. The 10 remaining states were eventually readmitted between 1868 and 1870 during the 40th and 41st United States Congresses.