Green MP Kevin Hague is leaving Parliament.
Mr Hague has announced he will be taking up the role of chief executive of environmental organisation Forest and Bird.
He has been a Green MP since 2008, and is currently the party's spokesperson on health, conservation and rainbow (LGBT) issues.
Mr Hague said there were still things he wanted to do in Parliament but, when Forest and Bird approached him, it was an opportunity he couldn't turn down.
"Well I think everyone knows I've been working pretty hard this year on some projects, like conservation funding, in fact, like trying to secure a national investigation into mental health services, and I had been intending to keep pushing ahead on those projects.
"What I'm going to need to do now is hand the baton for those projects over to someone else."
Mr Hague stood for the co-leadership of the party in 2015 but was unsuccessful, losing to James Shaw.
He admitted that was a blow.
"I was clear after that leadership contest I was disappointed not to win, but after that I sort of recommitted myself to the task and I think everyone will have seen that I have worked really hard in my portfolios and I've been proud to support Metiria and James in that leadership role.
"I think they are both doing a fantastic job."
Colleagues commend Hague's work
Green Party co-leader Metiria Turei said she was truly sorry Mr Hague was leaving Parliament, and he had made a huge contribution to the Green Party.
"At the same time we are delighted Kevin will continue his contribution to the environment at Forest and Bird.
"We know he will be a fantastic leader for this New Zealand icon."
Mr Shaw said Mr Hague had been an excellent advocate for Green policies over many years.
"He has worked tirelessly and effectively, for the Green Party and with other political parties.
"We will miss his passion and his wisdom," Mr Shaw said.
"Kevin's achievements in Parliament include championing accountability and workplace health and safety in the wake of the Pike River disaster, forcing culture change at ACC, helping establish Nga Haerenga (the New Zealand Cycle Trail), and successful campaigns for marriage equality and to save the Mokihinui River."
Ms Turei welcomed Mr Coates to Parliament as Mr Hague's replacement.
"Barry brings extensive experience in social justice, climate change and Pacific work, including 10 years as executive director of Oxfam New Zealand.
"He will be an important new voice in Parliament and we look forward to working with him."