Maori Party founder Tariana Turia will stand down at the next election.
She announced her decision on Friday, saying she wanted to give the party plenty of time to consider a replacement for the co-leadership position she has held since 2004.
"I have given it serious thought and have made the decision with my family not to seek re-election in 2014," she said.
"I am looking forward to spending more time with my husband and our mokopuna."
Mrs Turia's decision will be a blow to the party because she is its only MP with a safe seat in parliament.
Her co-leader, Pita Sharples, says he and Mrs Turia have steered the waka for the last eight years.
"It will be a huge change to lose my mate," he said.
"I totally support her decision, she will be leaving a legacy of opportunity for Maori."
The party's third MP, Te Ururoa Flavell, is almost certain to succeed Mrs Turia as co-leader.
He says she has shown inspiring leadership and absolute commitment.
Mrs Turia came to parliament as a Labour MP but quit the party over the Foreshore and Seabed Act and formed the Maori Party.
It has three MPs in parliament and has signed a support agreement with National.