In the United States, a contingent election is used to elect the president or vice president if no candidate receives a majority of the whole number of electors appointed. A presidential contingent election is decided by a special vote of the United States House of Representatives, while a vice-presidential contingent election is decided by a vote of the United States Senate. During a contingent election in the House, each state delegation votes en bloc to choose the president instead of representatives voting individually. Senators, by contrast, cast votes individually for vice president.

The contingent election process is specified in Article Two, Section 1, Clause 3 of the United States Constitution. The procedure was modified by the Twelfth Amendment in 1804, under which the House chooses one of the three candidates who received the most electoral votes, while the Senate chooses one of the two candidates who received the most electoral votes. The phrase "contingent election" is not in the text of the Constitution but has been used to describe this procedure since at least 1823.

Contingent elections have occurred three times in American history: in 1801, 1825, and 1837. In 1800, Thomas Jefferson and Aaron Burr, the presidential and vice-presidential nominees on the ticket of the Democratic-Republican Party, received the same number of electoral votes. Under the pre-Twelfth Amendment Constitution, a contingent election was held the following year to decide which one would be president and which vice president. In 1824, the Electoral College was split between four presidential candidates, with Andrew Jackson losing the subsequent contingent election in the House to John Quincy Adams even though he won a plurality of both the popular and electoral vote. In 1836, faithless electors in Virginia refused to vote for Martin Van Buren's vice presidential nominee, Richard Mentor Johnson, denying him a majority of the electoral vote and thus forcing a contingent election in the Senate for vice president; Johnson won the election handily.

The past three contingent elections were conducted by the outgoing Congress because congressional terms then ended / began on March 4, the same day as presidential terms. In 1933, the Twentieth Amendment set the new congressional term to start on January 3 and the new presidential term on January 20. The amendment shortened the length of lame-duck sessions of Congress by two months, and any future contingent elections would be conducted by the incoming Congress.

In the United States, the president and vice president are indirectly elected by the Electoral College, which, since ratification of the Twenty-third Amendment in 1961, consists of presidential electors from the 50 states and the District of Columbia. The 538 electors that make up the Electoral College are directly elected by their respective states. Since the election of 1824, most states have chosen their electors on a statewide winner-take-all basis, based on the statewide popular vote on Election Day. Maine and Nebraska are the two exceptions, with both states allocating electors by congressional district. Although ballots list the names of the presidential and vice presidential candidates (who run together as a ticket), voters actually choose electors when they vote for president and vice president. The presidential electors in turn cast electoral votes for the two offices. Electors normally pledge to vote for their party's nominee, but some "faithless electors" have voted for other candidates.

A candidate must receive an absolute majority of electoral votes (currently 270) to win the presidency or the vice presidency. If no candidate receives a majority in the election for president or vice president, that election is determined via the contingency procedure in the 12th Amendment. In this case, the House chooses the president from among the top three presidential electoral vote-getters, and the Senate chooses the vice president from among the top two vice presidential electoral vote-getters.

Section 3 of the Twentieth Amendment specifies that if the House of Representatives has not chosen a president-elect in time for the inauguration (noon on January 20), then the vice president-elect becomes acting president until the House selects a president. Under the Presidential Succession Act of 1947, the Speaker of the House will become acting president until either the House selects a president or the Senate selects a vice president. As of 2025, none of these circumstances have ever occurred. The Constitutional silence on this point could have caused a constitutional crisis in the 1801 contingent election, when the House of Representatives was temporarily unable to resolve the Jefferson–Burr Electoral College deadlock.

If no candidate for president receives an absolute majority of the electoral votes, pursuant to the Twelfth Amendment, the House of Representatives must go into session immediately to choose a president from among the three candidates who received the most electoral votes. Each state delegation votes en bloc, with each having a single vote. A candidate must receive an absolute majority of state delegation votes (currently 26 votes) to become president-elect. The House continues balloting until it elects a president. As a consequence of the en bloc voting, the party that holds the majority in the House could lose the contingent election if the minority party holds the majority of state delegations. The District of Columbia, which is not a state, does not participate; the Twenty-third Amendment, which granted electoral votes to the district, does not grant the District of Columbia a vote in contingent elections.