The chairwoman of the Democratic National Committee (DNC) Debbie Wasserman Schultz has resigned amid a leak of internal DNC emails showing officials actively favoured Hillary Clinton over Bernie Sanders during the presidential primary.
In a statement, Ms Schultz said the best way for the party to accomplish its goal of putting Mrs Clinton in the White House was for her to step aside after the convention, which starts in Philadelphia on Monday.
Mr Sanders, who has frequently accused the party of playing favourites, had demanded that Ms Schultz resign.
The cache of emails leaked by the Wikileaks website disclosed that DNC officials explored ways to undermine Mr Sanders' insurgent presidential campaign, including raising questions about whether the senator from Vermont, who is Jewish, was really an atheist.
Mr Sanders said Ms Schultz, a US representative from Florida, had made the right decision for the future of the Democratic Party.
"The party leadership must also always remain impartial in the presidential nominating process, something which did not occur in the 2016 race," he said.
The DNC said on Twitter that vice-chairwoman Donna Brazile will serve as interim chair throughout the election.
The leaked emails angered Mr Sanders' supporters, hundreds of whom took to the streets of Philadelphia on Sunday to voice their discontent.
Sanders supporter Gwen Sperling said: "It just validated everything we thought, everything we believed to be true, that this was completely rigged right from the beginning, and that you know it was really about what theywere doing everything to set it up so she would win."