Kevin Rudd will stand against Prime Minister Julia Gillard in Monday's Labor Party leadership ballot, he has confirmed.
He wanted to ''restore the trust'' of the Australian people that she had lost, he told a news conference.
Ms Gillard, who ousted him as PM in June 2010, called the vote following weeks of speculation that he would challenge her for the top job.
Mr Rudd resigned as foreign minister in Washington DC late on Tuesday night.
Speaking to reporters in Brisbane just hours after returning from the United States, he said he wanted to get back to doing the job that the Australian people had elected him to do.
Mr Rudd won the 2007 election by a landslide and remains popular in opinion polls.
He called for a ''truly secret'' ballot and also said that if he failed to win the majority vote from his colleagues, he would go to the backbenches.
''I will not challenge Julia a second time; I will continue to work for my community,'' he said.
Ms Gillard, announcing the ballot on Thursday, also made the same pledge if unsuccessful in Monday's ballot.