Julia Gillard, the Australian prime minister, has been unseated by intra-party rival Kevin Rudd as the Labor Party leader.
Gillard lost a snap party ballot on Wednesday.
She had called for the vote amid speculation that supporters of Rudd were preparing to challenge her. Ultimately, Rudd won the vote of the Labor caucus by 57 votes to Gillard's 45, the official returning officer announced.
Gillard, then Rudd's deputy, had toppled the former prime minister in a leadership coup in June 2010. In the months following that political coup, Gillard was elected as Australia's first female prime minister, and she subsequently picked Rudd to serve as her foreign minister.
Rudd resigned from his post as foreign minister in February 2012, saying that he felt he no longer had his PM's support. A failed party leadership bid followed, but he was finally able to seal his return to the top post in the party after Wednesday's vote.
Gillard had earlier pledged to quit politics if she lost the party leadership vote. Opinion polls suggested she was headed for defeat in general elections slated for September.