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.
Who wants to be leader?
Andrew Little
Lawyer and former EPMU boss in his second term as a list MP. Nominated by Iain Lees-Galloway, who backed David Cunliffe, and Christchurch East MP Poto Williams. Likely to win strong union support and possibly some Cunliffe supporters in the caucus. Twitter followers: 3065
Nanaia Mahuta
Hauraki-Waikato MP and former minister who has been in Parliament since 1996. Ran on Cunliffe's ticket for his failed bid in 2011. Nominated by Manurewa MP Louisa Wall and Mangere MP Su'a William Sio and should get some of the Maori caucus' six votes. Twitter followers: 982
David Parker
Cunliffe's deputy, former Attorney-General and MP since 2002. Making his second bid for the leadership. Nominated by Manukau East MP Jenny Salesa and West Coast MP Damien O'Connor. Twitter followers: 284
Grant Robertson
Wellington Central MP since 2008 and former leader David Shearer's deputy. Likely to win the most votes in caucus but won only 25 per cent of members' vote in his last bid and even less of the union vote. Twitter followers: 9849
