The Hauraki-Waikato MP discussed her potential bid with Maori caucus colleagues earlier yesterday before deciding to go ahead late in the day and confirming it just half an hour before the 5pm deadline.
"This decision has been made with the knowledge that as the party reviews the election outcome, we can learn from the base of support that was demonstrated across Maori electorates, in South Auckland and among Pacific and ethnic communities."
Labour's review of its worst election defeat in 92 years begins shortly and Ms Mahuta said "some of the solutions lie within the constituency base that I represent - certainly South Auckland and the Pacific vote".
Ms Mahuta's rivals are former deputy leaders David Parker and Grant Robertson and former union boss Andrew Little - a trio of white male contenders that left the party facing criticism for a lack of diversity in its leadership.
Ms Mahuta said her rivals all had something to offer, "but certainly the party is looking at a different way of doing things and I think I offer a difference". She was hopeful of one day becoming New Zealand's first Maori Prime Minister, "but one step at a time".
Her announcement came at the end of another tumultuous day in the saga of the Labour leadership contest which began with former leader David Shearer lashing out at his successor David Cunliffe for disloyalty. Ms Mahuta was Mr Cunliffe's running mate in his unsuccessful 2011 tilt at the Labour leadership which was won by Mr Shearer and she has remained loyal to him since.
The nominees backing her candidacy were two other camp Cunliffe caucus members, Sua William Sio and Louisa Wall, who both backed Mr Cunliffe's bid to regain the leadership which he withdrew this week.
Ms Mahuta said she had not discussed her bid with Mr Cunliffe.
Mr Cunliffe yesterday said Mr Shearer's criticism of him was "absolute nonsense ... very unfortunate and very disappointing".
Without making it clear whether she was referring to Labour's polling or its internal tensions, Ms Mahuta said the leadership contest could be rocky.
"Things may get worse before they get better but I'm up for it ... changes need to happen."
Despite having discussed her bid with Labour's Maori caucus, she was not taking their support for granted.
"What I do know is that the Maori and Pacific caucus are a key part of the future of the Labour Party."
But earlier yesterday Mr Shearer had a different take on what Labour needed to do.
"If you look at the last three elections you will see the people that walked away from Labour were middle New Zealanders, white blokes. They walked away from us in great numbers and we need to win them back. If we don't do that, we won't get ahead."
He also said Labour had to confront issues around ensuring more democratic union representation in its leadership selection process.
Meanwhile, commenting on rival contender Mr Little's suggestion that Labour's deputy leader should be a woman, Mr Parker said he would instead support the most suitable candidate for that role if he won.
"I will be going for competence in every position I appoint whether it's deputy or anyone else and I would note that I think Helen Clark would be horribly offended to think that she achieved the position of being one of the best prime ministers we've had in New Zealand on the basis of her gender."
Mr Little, who was endorsed by Mr Cunliffe this week, said he had not heard from him about whether he was considering changing his endorsement to back Ms Mahuta instead. "It hasn't been retracted or removed."
He said Ms Mahuta's surprise entry would have an impact on the vote.
- By Adam Bennett of the New Zealand Herald
