The 45th United States Congress was a meeting of the legislative branch of the United States federal government, consisting of the United States Senate and the United States House of Representatives. It met in Washington, D.C. from March 4, 1877, to March 4, 1879, during the first two years of Rutherford Hayes's presidency. The apportionment of seats in the House of Representatives was based on the 1870 United States census. The Senate had a Republican majority, and the House had a Democratic majority.

The presidency of Rutherford B. Hayes began on March 4, 1877, when Rutherford B. Hayes was inaugurated as President of the United States, and ended on March 4, 1881. Hayes became the 19th president, after being awarded the closely contested 1876 presidential election by Republicans in Congress who agreed to the Compromise of 1877. That Compromise promised to pull federal troops out of the South, thus ending Reconstruction. He refused to seek re-election and was succeeded by James A. Garfield, a fellow Republican and ally.