Here is a wrap of Kevin Rudd's speech after the leadership ballot, and you can find out what Julia Gillard had to say here: Gillard says won't recontest Lalor.
New Labor leader Kevin Rudd says the negativity and destructive politics at the federal level must stop.
Mr Rudd said politics in recent times had "failed the Australian people" and he was driven by a need to secure the nation's future.
"I simply do not have it in my nature to stand idly by and allow an Abbott government to come to power in this country by default," he said.
"I recognise that Mr Abbott is a man steeped in the power of negative politics and he is formidable at negative politics.
"But I see no evidence of a real positive plan for our country's future."
Mr Rudd also thanked outgoing treasurer Wayne Swan for his contribution to the government.
He said he had worked "intimately" with Mr Swan in 2008-2009 to prevent the country from rolling into the global economic recession.
"So Wayne, whatever our differences have been, I acknowledge that contribution here as part of that team which kept us out of global catastrophe," Mr Rudd said.
New Labor deputy leader Anthony Albanese said he had a big job to do.
"I will do it with enthusiasm, passion and commitment and give my all for the cause of Labor," he said, standing side by side with Mr Rudd.
"It is only Labor governments, I believe, that can truly serve the long term interests of the nation."
Mr Albanese said on Wednesday night the party had maximised its chances of going into a third term of a Labor government.
He paid tribute to Ms Gillard and Mr Swan for their achievements and for their efforts in ensuring Labor was able to govern since the hung parliament in 2010.
Mr Rudd issued a call to Australia's youth, many of whom he said had shunned an interest in the nation's political system.
"I understand why you've switched off, it's hardly a surprise," he said.
"But I want to ask you to please come back and listen afresh.
"We need you, we need your energy, we need your ideas, we need your enthusiasm and we need you to support us in the great challenges which lie ahead for the country.
"And with your energy, we can start cooking with gas."
Source: AAP
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EARLIER: LIVE BLOG
11.05pm: Opposition leader Tony Abbott congratulates Kevin Rudd and blames "the faceless men" for the leadership spill. "You deserve better than this," Mr Abbott told voters.
10.49pm: New Labor deputy leader Anthony Albanese said he had a big job to do. "I will do it with enthusiasm, passion and commitment and give my all for the cause of Labor," he said, standing side by side with Mr Rudd.
10.48pm: Kevin Rudd also thanked outgoing treasurer Wayne Swan for his contribution to the government. He said he had worked "intimately" with Mr Swan in 2008-2009 to prevent the country from rolling into the global economic recession.
10.45pm: Kevin Rudd says politics in recent times had "failed the Australian people" and he was driven by a need to secure the nation's future.
"I simply do not have it in my nature to stand idly by and allow an Abbott government to come to power in this country by default," he said.
10.39pm: Kevin Rudd addresses the media, saying Julia Gillard left a great legacy, as she "has been a woman of extraordinary intelligence, of great strength, and great energy... She has been a remarkable reformer."
10.36pm: Watch Wayne Swan's full speech post leadership ballot.
10.34pm: Watch the speech Julia Gillard delivered after being defeated at the Labor leadership ballot.
10.29pm: Experts say tonight's result leaves critical constitutional questions over whether an early election will be called.
10.06pm: Julia Gillard has tendered a letter to the governor general resigning as Prime Minister.
10pm: Julia Gillard is now at Government House to resign after losing the Labor leadership.
9.50pm: Kevin Rudd is expected to speak at 10pm.
9.30pm: Deputy PM Wayne Swan is making a statement now, saying he's proud of the record of the Labor government he has served, and it has been a privilege to serve as deputy to Julia Gillard. He does intend to recontest Tens of thousands of ordinary Australians have been asking me to do this for a long time."
5.10pm: No sign yet of Kevin Rudd, but it seems like he won't be far away.
5.04pm: Meanwhile, on the other side of politics, Tony Abbott has been spotted out getting some evening exercise and Christopher Pyne has picked an interesting day to join Twitter.
5.02pm: Just about every journalist in Canberra is gathered in Labor's caucus room in Parliament House, expecting Kevin Rudd to arrive any moment.
4.58pm: Bob Carr has reportedly delayed his planned trip to Indonesia.
4.45pm: There are reports Kevin Rudd will make a statement at 5pm.
4.40pm: Some Labor figures are making their preferences clear. Kate Lundy tweeting she'll be supporting Julia Gillard.
4.20pm: Julia Gillard has called a leadership ballot for 7pm tonight. She says the loser should retire from politics.
4.15pm Prime Minister Julia Gillard has called a special caucus meeting for 7pm tonight to allow another vote on the leadership against expected contender Kevin Rudd.
Ms Gillard says that it means if she lost she would leave federal politics. She said it's in the best interests of the nation and the ALP for the matter to be resolved.
Asked if this meant that if she lost she would leave federal politics Ms Gillard said: "Correct".
"This is it," Ms Gillard told Sky News. "I am asking my party to endorse me."
3.50pm SkyNews sources are also reporting Foreign Minister Bob Carr will not be going to Indonesia tomorrow.
3.40pm SkyNews is reporting a caucus petition to force a challenge to Prime Minister Julia Gillard has been circulated.
3.15pm Prime Minister Julia Gillard has told parliament she is getting on with the job, after Opposition Leader Tony Abbott questioned her about her leadership.
Mr Abbott asked Ms Gillard if, given the "paralysis" gripping the government over her leadership, she would call an earlier election on August 3.
"I can assure him and I can assure the Australian people that as prime minister I am getting on with the job and that is what the government is doing," she told the house during question time on Wednesday.
2.45pm So far, no Labor MP has confirmed they have seen the petition.
2.30m Mr Abbott then moved a motion to suspend standing orders and called on the government to "end its internal arguments and actually get on with governing this country."
1.52pm: Bill Shorten has not changed his position, according to a statement from his office.
1.40pm: ABC journalist Latika Bourke says she can't find "a single Labor MP who has seen or signed" a petition said to be circulating to gather supporters for Kevin Rudd, ahead of a rumoured leadership spill.
1.38pm: The Minister for Resources and Energy, Gary Gray, has told reporters at Parliament House his support is still with Julia Gillard.
"Every knows I support the Prime Minister enormously," he said. He refused to elaborate on further questions.
Mr Gray was appointed to the federal cabinet in the reshuffle that followed failed calls for a Labor leadership spill in March this year.
1.15pm: There are claims from both sides that powerbroker Bill Shorten is "shifting away from the Prime Minister," according to the Financial Review.
Just five days ago, former Prime Minister Kevin Rudd hosed down rumours that another Labor leadership spill was at hand and that Mr Shorten had contacted him to offer support.
EARLIER:
A leadership spill is looking more likely with supporters of Kevin Rudd reportedly circulating a caucus petition to force a challenge to Prime Minister Julia Gillard.
There are also reports that a ballot could be held at 9am on Thursday.
Mr Rudd is under pressure from his caucus supporters to make a move in the dying days of the current parliament ahead of the September 14 election.
Any move against Ms Gillard will first require a petition, signed by at least a third of the caucus, for a special meeting. A separate ballot would be required for a leadership spill.
If a spill occurs, independent Tony Windsor says he won't rule out switching to the coalition if there is any leadership change.
Mr Windsor and fellow independent Rob Oakeshott gave Ms Gillard the numbers to form a minority government after the 2010 election.
"If the Labor Party can't get its mess together, there may be a scenario where ... Tony Abbott, may in fact receive my vote," he told reporters in Canberra on Wednesday.
"If it came back to the house, to test the confidence, I wouldn't guarantee the challenger that it would naturally flow that my support would be that way."
But maverick independent Bob Katter - who after the 2010 election gave his support to the coalition - on Wednesday said he would back Mr Rudd, a fellow Queenslander and a personal friend.
"Prior to the ALP caucus meeting I advise that if, and only if, caucus selects Kevin Rudd then I will provide a vote of confidence to facilitate his election as leader," Mr Katter told reporters in Canberra.
"The problem is that noone is driving the bus."
Mr Katter, who has formed his own party to contest the September 14 election, said his decision to back Mr Rudd would be in "the nation's interest" and he did not want to "condemn Australia to a landslide election" win for the coalition.
Shadow Treasurer Joe Hockey attacked Mr Katter's decision.
"Bob Katter shouldn't be propping up an awful Labor Govt. They are a circus and continue to focus on their own jobs rather than Aussie jobs," Mr Hockey tweeted.
The Australian Greens, whose sole MP in the lower house is deputy leader Adam Bandt, have flagged they would not support the opposition.
"The only people who can determine confidence are the parliament of Australia or the people," she told reporters in Canberra on Wednesday.
"We are saying we will do nothing to facilitate Tony Abbott getting into the prime minister's position."
Backers of the prime minister have challenged him to make the move.
"The ball's in Mr Rudd's court. The prime minister is not going to stand down," cabinet minister Greg Combet said earlier on Wednesday.
In March, Mr Rudd refused to stand after Ms Gillard called a leadership spill.
