The Green Party has dealt an unexpected blow to Labour's chances of winning the hotly contested Wellington seat of Ohariu by deciding at the 11th hour to stand a candidate.

Tane Woodley was the surprise revelation at an Ohariu candidates meeting in the suburb of Khandallah on Wednesday night - revealing to the crowd that he was entering the race following the shock departure of 33-year incumbent Peter Dunne.

Woodley planned to campaign solely for the party vote. But the decision is likely to benefit National's Ohariu candidate Brett Hudson, as it could split the vote on the left and dent the lead in the polls enjoyed by Labour's Greg O'Connor.

On the last round of polling, O'Connor was sitting on a 10-point advantage ahead of Dunne.

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The Greens had initially decided not to stand a candidate to boost O'Connor's chances of unseating Dunne. Woodley ran in Ohariu at the last election and picked up 2764 electorate votes.

STUFF Labour Ōhāriu candidate Greg O'Connor and National Ōhāriu candidate Brett Hudson reacts to the news the Greens will now stand in the electorate.

Dunne won the seat in 2014 by a margin of just 710. But with his UnitedFuture Party no longer in the running, the seat is no longer strategic to the overall makeup of Parliament.

It was now fair game to contest the party vote, the Greens said.

"Our original decision to not stand a candidate in Ohariu was because we wanted to unseat Peter Dunne. That gave us the best chance at our level - the electorate level - of changing the Government," Woodley said.

STACEY KIRK/STUFF Green Party candidate Tane Woodley has been revealed as the shock last-minute contender for the Ohariu seat.

"Since he decided not to stand, that situation's come about and now we have the opportunity to push hard for the party vote."

Woodley acknowledged his presence on the Ohariu ballot would likely eat into O'Connor's share of the vote.

"I think it will have an effect - people will vote for me. But I'm not chasing the electorate vote, I don't think it will tip the balance. I think Greg will still have the advantage."

RNZ James Shaw discusses with Susie Ferguson the decision to stand a candidate in Ohariu.

O'Connor said at the candidates' meeting: "Nothing surprises me in this election.

"I would imagine that there'll be probably five other announcements that are going to be as significant as this one, the way things are going.

"So we just have to roll with the punches, just keep on and get as many votes as we can."

CAMERON BURNELL/STUFF The withdrawal of long-serving Ohariu MP Peter Dunne from the electorate race this year has prompted the Green Party to submit a late candidate.

Hudson would not be drawn on whether Woodley's decision to run would increase his chances.

"This will probably give, I think, the people of Ohariu a chance to reassess the options.

"I'm just going to be campaigning hard for a two-tick campaign."

MAARTEN HOLL/STUFF Woodley's presence on the ballot paper is likely to harm the aspirations of Labour's Greg O'Connor in Ohariu.

Woodley said there were many problems facing the electorate, which were relevant nationally.

"In terms of poverty, in terms of water quality, climate change transport. National as a Government has shown that it's not ready and it's not able to tackle those problems - their response is to ignore it and let it turn into a crisis," Woodley said.

In 2014, Woodley's campaigning in Ohariu earned the Greens 5623 party votes. The party is fighting for its survival in Parliament after recent polls put it below the five per cent threshold.

STUFF National's candidate Brett Hudson could benefit from Woodley's inclusion in the Ohariu race.

They had informed Labour of their intentions under the Memorandum of Understanding between the two parties.

The party's co-convenor Debs Martin said Woodley's inclusion was not expected to dent Labour's campaign.

"With Peter Dunne making the decision to retire from Parliament, the way was open again for us to campaign hard for the party vote. In addition this won't have any material effect on the campaign that Labour is running".

Woodley, who has ancestry from Tuhoe and the West Coast, lives in Johnsonville with his wife and children. He is a former army officer with a masters in international relations.

Ohariu has been in the spotlight since a poll emerged showing Dunne was likely to lose the seat. The veteran MP and minister then announced his retirement, revealing he no longer had the motivation for the fight it was shaping up to be.

It threw a spanner into the electorate deal he shared with National. Hudson is now in the throes of raising his public profile in the month before the election after weeks of trying not to steal Dunne's spotlight.

* Audio courtesy of Radio NZ