The 1924 Democratic National Convention, held at the Madison Square Garden in New York City from June 24 to July 9, 1924, was the longest continuously running convention in United States political history. It took a record 103 ballots to nominate a presidential candidate. It was the first major party national convention that saw the name of a woman, Lena Springs, placed in nomination for vice president. John W. Davis, a dark horse, eventually won the presidential nomination on the 103rd ballot, a compromise candidate following a protracted convention fight between distant front-runners William Gibbs McAdoo and Al Smith.

Davis and his vice presidential running-mate, Governor Charles W. Bryan of Nebraska, went on to be defeated by the Republican ticket of President Calvin Coolidge and Charles G. Dawes in the 1924 presidential election.

New York had not been chosen for a convention since 1868, and its selection as the site for the 1924 convention was based in part on the state party's recent success. Two years earlier, thirteen Republican congressmen had lost their seats to Democrats. Wealthy New Yorkers, who had outbid other cities, declared their purpose "to convince the rest of the country that the town was not the red-light menace generally conceived by the sticks". Though "dry" organizations that supported continuing the prohibition of alcohol opposed the choice, in the fall of 1923 it won the grudging consent of McAdoo, a dry, before McAdoo's connection to the Teapot Dome scandal made Smith a serious threat. (McAdoo's candidacy was hurt by the revelation that he had accepted money from Edward L. Doheny, an oil tycoon implicated in Teapot Dome.) McAdoo's adopted state, California, had played host to the Democrats in 1920.

McAdoo swept the primaries in the first real race in the history of the party, although most states chose delegates through party organizations and conventions, giving most of their projected votes to local or hometown candidates, referred to as "favorite sons".

The Ku Klux Klan had surged in popularity after World War I, due to its leadership's connections to passage of the successful Prohibition Amendment to the U.S. Constitution. This made the Klan a political power throughout many regions of the United States, and it reached the apex of its power in the mid-1920s, when it exerted deep cultural and political influence on both Republicans and Democrats. Its supporters had successfully quashed an anti-Klan resolution before it ever went to a floor vote at the 1924 Republican National Convention earlier in June, and proponents expected to exert the same influence at the Democratic convention. Instead, tension between pro- and anti-Klan delegates produced an intense and sometimes violent showdown between convention attendees from the states of Colorado and Missouri. Klan delegates opposed the nomination of New York governor Al Smith because Smith was a Roman Catholic and an opponent of Prohibition, and most supported William Gibbs McAdoo. Non-Klan delegates, led by Sen. Oscar Underwood of Alabama, attempted to add condemnation of the organization for its violence to the Democratic Party's platform. The measure was narrowly defeated, and the anti-KKK plank was not included in the platform.

Smith's name was placed into nomination by Franklin D. Roosevelt, in a speech in which Roosevelt dubbed Smith "The Happy Warrior". Roosevelt's speech, which has since become a well-studied example of political oratory, was his first major political appearance since the paralytic illness he had contracted in 1921. The success of this speech and his other convention efforts in support of Smith signaled that he was still a viable figure in politics, and he nominated Smith again in 1928. Roosevelt succeeded Smith as governor in 1929, and went on to win election as president in 1932.

The first day of balloting (June 30) brought the predicted deadlock between the leading aspirants for the nomination, William G. McAdoo of California and Gov. Alfred E. Smith of New York, with the remainder divided mainly between local "favorite sons". McAdoo was the leader from the outset, and both he and Smith made small gains in the day's fifteen ballots, but the prevailing belief among the delegates was that the impasse could only be broken by the elimination of both McAdoo and Smith and the selection of one of the other contenders; much interest centred about the candidacy of John W. Davis, who also increased his vote during the day from 31 to 61 (with a peak of 64.5 votes on the 13th and 14th ballots). Most of the favorite son delegations refused to be stampeded to either of the leading candidates and were in no hurry to retire from the contest.

In the early balloting many delegations appeared to be jockeying for position, and some of the original votes were purely complimentary and seemed to conceal the real sentiments of the delegates. Louisiana, for example, which was bound by the "unit rule" (all the state's delegate votes would be cast in favor of the candidate favored by a majority of them), first complimented its neighbor Arkansas by casting its 20 votes for Sen. Joseph T. Robinson, then it switched to Sen. Carter Glass, and on another ballot Maryland Gov. Albert C. Ritchie got the twenty, before the delegation finally settled on John W. Davis.