The 1920 United States presidential election was the 34th quadrennial presidential election, held on Tuesday, November 2, 1920. In the first election held after the end of World War I and the first election after the ratification of the Nineteenth Amendment, Republican Senator Warren G. Harding of Ohio defeated Democratic Governor James M. Cox of Ohio.

Incumbent Democratic President Woodrow Wilson privately hoped for a third term, but party leaders were unwilling to re-nominate the ailing and unpopular incumbent. Former President Theodore Roosevelt had been the front-runner for the Republican nomination, but he died in 1919 without leaving an obvious heir to his progressive legacy. With both Wilson and Roosevelt out of the running, the major parties turned to little-known dark horse candidates from the state of Ohio, a swing state with a large number of electoral votes. Cox won the 1920 Democratic National Convention on the 44th ballot, defeating William Gibbs McAdoo (Wilson's son-in-law), A. Mitchell Palmer, and several other candidates. Harding emerged as a compromise candidate between the conservative and progressive wings of the party, and he clinched his nomination on the tenth ballot of the 1920 Republican National Convention.

The election was dominated by the American social and political environment in the aftermath of World War I, which was marked by a hostile response to certain aspects of Wilson's foreign policy and a massive reaction against the reformist zeal of the Progressive Era. The wartime economic boom had collapsed and the country was deep in a recession. Wilson's advocacy for America's entry into the League of Nations in the face of a return to non-interventionist opinion challenged his effectiveness as president, and overseas there were wars and revolutions. At home, the year 1919 was marked by major strikes in the meatpacking and steel industries and large-scale race riots in Chicago and other cities. Anarchist attacks on Wall Street produced fears of radicals and terrorists. The Irish Catholic and German communities were outraged at Wilson's perceived favoritism of their traditional enemy Great Britain, and his political position was critically weakened after he suffered a stroke in 1919 that left him severely disabled.

Harding all but ignored Cox in the race and essentially campaigned against Wilson by calling for a "return to normalcy". Harding won a landslide victory, sweeping every state outside of the South and becoming the first Republican since the end of Reconstruction to win a former state of the Confederacy, Tennessee. Harding's victory margin of 26.2% in the popular vote remains the largest popular-vote percentage margin in presidential elections since the unopposed re-election of James Monroe in 1820, though other candidates have since exceeded his share of the popular vote. Cox won just 34.1% of the popular vote, and Socialist Eugene V. Debs won 3.4%, despite being in prison at the time. It was also the first election in which women had the right to vote in all 48 states, which caused the total popular vote to increase dramatically, from 18.5 million in 1916 to 26.8 million in 1920. Both vice presidential nominees would eventually become president in their own right (which had never happened before or since): Harding died in 1923 and was succeeded by Vice President Calvin Coolidge, while the Democratic vice presidential nominee, Franklin D. Roosevelt, would eventually win an unprecedented four consecutive presidential elections starting in 1932, dying shortly into his fourth term. This is the only election in history where the losing presidential candidate never became President but the losing vice presidential candidate later did.

The 1920 Republican National Convention nominated Ohio Senator Warren G. Harding for president and Massachusetts Governor Calvin Coolidge for vice president. The convention was held in Chicago, Illinois, at the Chicago Coliseum from June 8 to June 12, 1920, with 940 delegates. Under convention rules, a majority plus one, or at least 471 of the 940 delegates, was necessary for a nomination.

Many Republicans sought the presidential nomination, including General Leonard Wood, Illinois Governor Frank Lowden and California Senator Hiram Johnson. Dark horse Harding, however, was nominated. Many wanted to nominate Wisconsin Senator Irvine L. Lenroot for vice president, but Coolidge was nominated instead, because he was known for his response to the Boston Police Strike in 1919.

The convention also adopted a platform opposed to the accession of the United States to the League of Nations. The plank was carefully drawn up by Henry Cabot Lodge to appease opponents of the League such as Johnson, while still allowing eventual American entry into the League.