Bill Shorten has confirmed his candidacy for the federal Labor leadership, declaring the party can win the next election and has a mandate to protect the carbon price.
He says the party cannot afford to "bide its time" in opposition and allow the incoming Coalition government to "tear down" Labor's accomplishments of the past six years.
"I want to lead the rebuilding of our movement and to take the fight up to the Coalition in Australian politics," Mr Shorten told reporters in Melbourne.
"I am running because I believe that Labor can win the next election.
"I bring energy, I bring optimism, I'm hungry for victory, and these are qualities which are important to make Labor competitive to win the next election."
Mr Shorten, the former education minister, has indicated that if successful, his deputy would be Sydney-based MP Tanya Plibersek.
It is unclear at this stage whether Mr Shorten will be challenged for the position by former deputy prime minister Anthony Albanese.
If there is more than one candidate, the leadership will be decided through a ballot process involving parliamentary members as well as grassroots Labor members.
"I welcome rank and file participation," Mr Shorten said.
"I shall submit myself to my Caucus colleagues and to thousands of Labor Party members across Australia, and I welcome this ballot and the opportunity to start the momentum so that Labor can win the next election."
Mr Shorten has already indicated his view on how the party should approach the vexed issue of carbon pricing, given the Coalition's argument that it has a mandate to repeal Labor's policy.
He says that while the party's position will ultimately be determined by the new Caucus, Labor "fundamentally believes" in putting a price on carbon.
"Labor has a mandate for its views on carbon pricing pollution," he said.
Some in the party - including Richard Marles and Nick Champion - have suggested Labor should recognise the Coalition's election victory and allow it to implement its own Direct Action policy.
But former attorney-general Mark Dreyfus says pricing carbon is the "right thing" to do, and the Coalition's policy should not be waved through the Senate.
Mr Shorten is praised by his colleagues for his work on helping to get the National Disability Insurance Scheme off the ground, but others are wary of his role in toppling Kevin Rudd as prime minister in 2010 and his move against Julia Gillard earlier this year.
He has defended his involvement in recent leadership changes, saying the party needed to take steps to remain competitive.
"It is very clear that I, along with all members of the Caucus, should accept some responsibility for the last few years," he said.
"Decisions were hard. I have always acted with the best interests of the Labor Party and the nation at stake."
Mr Shorten is married to Chloe Bryce, the daughter of the Governor-General Quentin Bryce.