Jeanette Fitzsimons has announced she will resign from Parliament next month after 13 years as an MP for the Green Party.
Ms Fitzsimons stepped down as the Greens' co-leader last year and signalled then that she would not stand in the 2011 general election.
She had had intended to retire in 2005, but the sudden death of the party's co-leader Rod Donald prompted her to change her decision and stay on through another election.
Ms Fitzsimons, 65, says she has loved and hated her time as an MP.
"I've hated the petty point-scoring and bickering that goes on in the House, the triviality, the character assassination. And I must admit at times, I've hated the extremely long hours that you have to work to do this job."
However, Ms Fitzsimons says she enjoyed chairing the Local Government and Environment Select Committee and negotiating with various governments.
She says she is looking forward to spending more time on her farm and with her grandchildren.
Green Party co-leader Russel Norman says Ms Fitzsimons' expertise and work ethic are legendary.
He says it is a challenge for anyone to match those standards, but a challenge the party will embrace.
Ms Fitzsimons will be replaced by Gareth Hughes, 28, an environmental advocate currently working for Greenpeace.
Tributes for MP
Prime Minister John Key paid tribute to Ms Fitzsimons, saying she has made an extraordinary contribution to New Zealand politics.
"She's blazed a trail for the Green Party into Parliament, along with the late Rod Donald. She's a politician, I think, that's always played the issue and not the person or the individual.
"She's had strong beliefs, particularly when it comes to the environment, but she's always communicated her views in a very professional way with a lot of humility."
Labour Party leader Phil Goff says Ms Fitzsimons' departure is a sad loss for Parliament, but he does not believe it will put the Green Party in any danger.
"They will get new blood, they will continue to rebuild. But I think everyone in Parliament would acknowledge the great work Jeanette has done and the very decent person that she is."