Updated 5.59pm: Russel Norman says he wouldn't be standing down as the Greens co leader if the election result had been different.

"This is something I've considered for some time, and over the summer break I've had a space to give it a lot of thought and think about my future, and I've decided this is the right thing to do."

Dr Norman will relinquish the leadership role at the party's AGM in May and he doesn't know whether he'll serve out a full term as an MP.

He's been co leader since 2006 and says he's seen a lot in that time.

"When I took over Don Brash was still the leader of the National Party, Helen Clark was the leader of the Labour Party. I'm into my 2nd National Party leader and 5th Labour leader so I've seen a lot of politics."

Dr Norman says it's time for him to find a new challenge and spend more time with his family.

Labour leader Andrew Little says he didn't see it coming.

"He's actually made some real gains for the Green Party, raised the number of MPs in Parliament, he's lifted the quality of their talk on economic issues, so it's a bit of a surprise but I understand his reasons."

Well wishes for the departing Green Party co-leader have also come from his main political foe.

Prime Minister John Key offered some kinds words to his opponent today.

"Mr Norman's got a young family, there's a lot of pressures on being a co-leader of a party, so I'm a little bit surprised, but we wish him all the best."

MORE: Full statement from Russel Norman

MORE: Metiria Turei: "Sad to lose my fellow captain"

Succession plans

Dr Norman's making no concrete commitments about whether he'll stay long term as an MP once his successor is chosen.

"Obviously we'll see how that plays out, my role is to support the Green Party in that process, we'll cross that bridge when we come to it, it's a long way down the track."

Co-Leader Metiria Turei's making it clear there won't be much in the way of overt politicking when it comes to selecting his successor.

"I should say now for the benefit of media, that the caucus has agreed not to comment on any potential candidates until the party makes it's decision in May. The party has made great decisions in the past and I expect they will do so again."

With two Green MPs already tipped as potential successors for Russel Norman, their likely future coalition partner says he can work with either.

Senior MP Kevin Hague and the party's newest face in Parliament, James Shaw, are expected to be the front-runners for the male co-leader's position.

Labour's Andrew Little will have to work closely with whomever the Greens choose - but he says that's no problem.

Mr Little says he has a good working relationship with most of the Green MPs and the two parties have three years ahead to get to know each other better before the next election.

Kevin Hague says today's too soon for him to make any comments about what he might do.