Green Party co-leader Jeanette Fitzsimons today confirmed she will stand down in June.
She told reporters she looked forward to being an active backbencher, and it was time to pass the leadership on to the younger generation.
Ms Fitzsimons has led the Greens since 1995.
She entered Parliament with former co-leader Rod Donald in 1996, and had expected to retire before last year's election.
She agreed to stay on after Mr Donald, 48, died suddenly in 2005 of viral myocarditis.
Russel Norman has now been her co-leader for nearly three years.
Party rules dictate the co-leaders must be a man and a woman, and MPs Sue Bradford and Meteria Turei today confirmed they would seek the candidacy when it opened next month.
The new co-leader would be appointed at the Green Party annual meeting on May 30-June 1.