The Mississippi Freedom Democratic Party (MFDP), also referred to simply as the Freedom Democratic Party, was an American political party that existed in the state of Mississippi from 1964 to 1968 during the Civil Rights Movement. Created as the partisan political branch of the Freedom Democrat organization (a contemporary Civil Rights activist group aligned with the national United States Democratic Party), the party was organized by African Americans and White Americans from Mississippi who were sympathetic to the Civil Rights Movement.

In Mississippi, African Americans were restricted from registering and voting by means of intimidation, harassment, terror, and complicated literacy tests. They had been limited from participation in the political system since 1890 by passage that year of a new state constitution, and by the practices of the governing white Democrats in the decades since, with participation in the state Democratic Party limited to whites. Starting in 1961, the Student Nonviolent Coordinating Committee (SNCC) and Council of Federated Organizations (COFO) had implemented campaigns to register black voters.

In June 1963, African Americans attempted to cast votes in the Mississippi primary election but were prevented from doing so. This contest to determine Democratic candidates was essentially the only competitive race, as the state was a de facto one-party jurisdiction under the control of the Mississippi Democratic Party. Unable to vote in the official election, an alternative "Freedom Ballot" was organized to take place at the same time as the scheduled November voting. With this election seen as a protest action to dramatize the denial of their constitutional voting rights, close to 80,000 people cast freedom ballots for an integrated slate of candidates. In response, James W. Wright, Fannie Lou Hamer, Ella Baker, and Bob Moses, founded the Mississippi Freedom Democratic Party in 1964. As a result, they encountered violent opposition that included activists being intimidated with church, home, and business burnings and bombings, beatings, and arrests.

With partial participation in the regular Mississippi Democratic Party blocked by segregationists, the COFO built on the success of the Freedom Ballot by formally establishing the MFDP in April 1964 as a non-discriminatory, non-exclusionary rival to the regular party organization. The MFDP hoped to become the officially recognized Democratic Party organization in Mississippi by winning the Mississippi seats at the 1964 Democratic National Convention for a slate of delegates elected by some black and white Mississippians.

Building the MFDP was a major thrust of the Freedom Summer project. After it proved to be impossible to register black voters against the opposition of state officials, Freedom Summer volunteers switched to building the MFDP using a simple, alternate process of signing up party supporters. This new process did not require people to take unfair literacy tests or to register for voting at the courthouse in public opposition to existing power structures.

By the end of August 1964, the Mississippi Freedom Democratic Party had gained so much attention nationally that its delegates had 80,000 members belonging to their racially integrated party.

In time, some activists from the Northeast, including some of the Freedom Riders, would come to dominate the administration of the new party.

On August 4, before the state convention, the bodies of James Chaney, Michael Schwerner and Andrew Goodman were discovered buried in an earthen dam. They had been workers with the Congress of Racial Equality (CORE), registering people to vote for the MFDP, and had been murdered for their activism. Missing for weeks since disappearing after investigating a church burning in June 1964, they were subjects of a massive manhunt that involved the FBI and United States sailors from a nearby base. The murders drew national attention and generated outrage, emboldening the MFDP to be the party to represent the state of Mississippi.