Kevin Rudd will be sworn in as Australian prime minister on Thursday,  three years and three days after he was ousted from the nation's leadership in an internal government showdown.

Julia Gillard tendered her resignation as prime minister to Governor-General Quentin Bryce Wednesday night after losing a ballot of ruling lawmakers to Rudd 57 votes to 45.

Bryce revealed she took late night legal advice on whether she should swear Rudd in as her replacement.

A minority government such as Gillard led has not been seen in Australian federal politics since World War II and the ruling Labor Party's  leadership change has raised unique constitutional questions.

While Rudd has the support of his party, he does not necessarily have the support of a majority of lawmakers in the 150-seat House of Representatives.

He could face a vote of no confidence before Parliament adjourns Thursday night for what is likely to be the last time before elections.

Gillard had set Sept. 14 as the election date. But Rudd has given no indication of whether he would stick with that timetable.

A loss of a no-confidence motion could trigger an election as early as Aug. 3.

Acting Solicitor-General Robert Orr wrote to Bryce that Rudd should be commissioned as prime minister.

Bryce's secretary Stephen Brady wrote that she wants an assurance from Rudd `` that he will announce his appointment at the first possible opportunity to the House of Representatives on order to give  the House the opportunity for whatever, if any, action it chooses to take.''

Wednesday's leadership ballot was forced by government lawmakers hoping to avoid a huge defeat in upcoming elections.

Gillard lacked Rudd's charisma, and although many Labor lawmakers preferred her style, her deepening unpopularity among voters compelled a majority to seek a change ahead of looming elections.

Labor depends on independents and a minor party for its fragile ruling coalition, but Rudd appeared capable of retaining it after two independent lawmakers who did not back Gillard's government said they would support his.

Rudd gave no indication of new policy directions or when he expected Australians would go to the polls.

``In 2007, the Australian people elected me to be their prime minister and that is a task I resume today with humility, with honor and with an important sense of energy and purpose,'' he said. (AP)