Labour's Hauraki-Waikato MP Nanaia Mahuta will contest the Labour Leadership.
Ms Mahuta said late this afternoon she had made the decision to stand after giving the matter serious consideration.
"This decision has been made with the knowledge that if the party reviews the election outcome, we can learn from the base of support that was demonstrated across Maori electorates in South Auckland and amongst Pacific and ethnic communities."
Ms Mahuta's announcement brings the number of contenders to replace David Cunliffe to four with former Deputy leader David Parker, Andrew Little and Grant Robertson also in the running.
Her candidacy announcement at 4.30pm came just before the deadline of 5pm.
She was one of the two MPs - the other being William Sio - to stand by former leader David Cunliffe yesterday when he announced he was withdrawing from the contest.
Last month former MP Tau Henare said the Labour Party owed it to its voters to elect a Maori leader or deputy leader.
Read more: David Shearer: Cunliffe should quit politics
Mr Henare said Labour won six of the seven Maori electorates. "The Maori voters on the weekend saved the Labour Party's backside and you would expect at least the deputy leader to be a Maori," he said last month.
He had tipped Ms Mahuta as someone who could take up the deputy leader position.
In July, Ms Mahuta attracted criticism for apparently making policy on the hoof. She had told the Marae programme that Labour would make te Reo compulsory in schools, which is not Labour's position.
Last year, she became a flag-bearer for working mothers when she called on the Speaker to consider new rules for MPs with children after voting rules required her to be in Parliament with her new-born daughter after midnight.
She complained to the Speaker: "No child should be in the workplace from nine 'til midnight."
She is also one of a small number of MPs to have a tattoo.
Ms Mahuta's run for the leadership comes just 24 hours after Mr Cunliffe's announcement that he was backing Andrew Little for leader.
Mr Little also revealed this afternoon that he had been nominated for the leadership by Christchurch East MP Poto Williams and Palmerston North MP Iain Lees-Galloway.