Sydney: On the eve of a crucial leadership ballot, Australian Prime Minister Julia Gillard on Sunday said she was "very confident" of a win to end the bitter challenge posed by Kevin Rudd and unite the ruling Labor party for the 2013 general election.

Gillard, who became Australia's first woman Prime Minister in June 2010 after she ousted Rudd, will face him in a secret ballot for the leadership tomorrow after he dramatically resigned as foreign minister while on a visit to the United States. He announced on Friday that he would challenge Gillard for the leadership post.

Soon after Rudd's surprise resignation on Wednesday, Gillard called a ballot on Monday to end the leadership speculation "once and for all."

Gillard, 50, arrived in Canberra on Sunday with her partner Tim Mathieson and said she was "very confident of the strong support of my colleagues."

"I believe Labor, every one of us, will unite after Monday's ballot. We will unite tomorrow and we will get our shoulders to the wheel delivering Labor's programme and plans," Gillard told reporters.

 "The important thing is that tomorrow's ballot ends this -- there is a result and following that result everyone accepts it and unites and gets on with the job and I am absolutely confident that will happen."

Gillard added she remained "convinced" that Labor could defeat Opposition Leader Tony Abbott at an election in 2013.

Meanwhile, Rudd, 54, today maintained he was the party's best chance of winning the next election, but pledged to support Gillard if he was rejected by caucus.

"If Julia Gillard is returned on Monday then she will have my unequivocal support between now and the next election because we have interests way beyond individuals here," he told Channel Nine.

Rudd said reports that he called the Prime Minister a "childless, atheist, former Communist" in Adelaide were wrong.

"I don't have any recollection of having said anything of the sort," he said.

Rudd said his hand was forced into his dramatic resignation from the foreign affairs portfolio in Washington as Gillard refused to "repudiate" comments made against him by senior ministers.

The former prime minister revisited the painful history that saw him deposed in 2010 and said he was given no warning that he was at risk of losing the party's confidence because his colleagues believed he was running a paralysed and chaotic government.

Rudd said he was doing his "absolute best" to steer Australia through the ravages of the global financial crisis and that his closest confidantes had ample opportunity to raise their concerns.

Meanwhile, based on current declarations of support in the 103-member caucus, The Australian newspaper said it believes Gillard has the backing of 67 members to Rudd's 31, with five MPs still undecided.

The Gillard camp believes the Prime Minister will receive up to 75 votes, while Rudd supporters say he is likely to end up with about 35 votes.