James Shaw is pinching himself after going from fighting for the Greens' survival just weeks ago to cracking dad jokes about his new ministerial role.

"It's nothing short of remarkable," he reflects, sitting beside an office window that looks across to the Beehive, which after a mammoth moving operation this weekend, will be filled with ministers from the Labour-led Government.

"There were moments early on in the campaign where I wasn't sure we were going to make it back in. I had a level of faith that we would. But sometimes there wasn't a lot of evidence for that."

Not only did the Greens return to Parliament with 6.3 per cent of the vote, but they are in Government for the first time in the party's history.

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It's an achievement that caps a turbulent campaign that saw MPs and key staff resign and Metiria Turei step down as co-leader after an admission of historic benefit fraud.

Now backing the Labour-NZ First coalition on confidence and supply, the Greens have secured policies including the introduction of a Zero Carbon Act, the establishment of an independent Climate Commission, and a Government-backed green technologies investment fund.

Read a summary of the Green-Labour agreement here.

Some are broadly outlined, such as a commitment to overhaul the welfare system and remove excessive sanctions on beneficiaries.

In the next three years New Zealanders will also vote in a referendum on legalising the personal use of cannabis - a jolt to years of conservative and slow reform of drug laws.

Jacinda Ardern has indicated the result could be binding, and Ross Bell, the NZ Drug Foundation's executive director, said if there was upfront debate leading into the referendum there was a good chance Kiwis could vote "Yes".

"I would assume Labour would not have committed to doing anything with the Greens unless they thought New Zealand First supported it too," Bell said. "And so the idea of the cannabis referendum...I think fundamentally it is also a New Zealand First thing as well."

Shaw, who is now Climate Change Minister, Statistics Minister and Associate Finance Minister, said the referendum and agreement to overhaul the welfare system bore Turei's imprint.

It was Turei who started a chain of events that threw her party into crisis but also changed the Government.

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Her decision to reveal in a speech to the party conference that she lied about how many flatmates were living with her to stop her benefit being cut while a young mother in the 1990s initially led to a surge in support for the Greens - Shaw tweeted "we got momentum, baby!" after the Greens reached 15 per cent in the 1 News Colmar Brunton poll.

Labour slumped and then leader Andrew Little revealed he had asked colleagues about whether he should step down. Two days later he did and people were soon talking about the "Jacinda effect".

One of Ardern's first acts as leader was to rule Turei out of Cabinet, and a bomb went off under the Greens' campaign when MPs David Clendon and Kennedy Graham revealed they would step down in protest at Turei remaining co-leader.

Shaw called a late-night media conference at Parliament, saying he felt betrayed and the MPs had violated the Greens' culture.

This week he stood on the same black and white tiles in Parliament, flanked by Minister for Women Julie Anne Genter, Conservation and Land Information Minister Eugenie Sage and Parliamentary Under-Secretary to the Minister of Justice Jan Logie.

Clendon and Graham were but an unpleasant memory. Shaw talked of presenting a bottle of Glenmorangie whiskey to Winston Peters the night before, and there were groans when he answered a question about why he wanted Statistics: "It's the only portfolio that counts."

Special votes brought in Golriz Ghahraman as a Green MP. She and Chloe Swarbrick are the young stars of the party, already organising a public picnic on Parliament's front lawn next week. More than 200 people have accepted a Facebook invite and a further 1700 shown interest in attending.

In Ardern, Labour has a Prime Minister able to pull off similar efforts - she hosts frequent Facebook Live events to answer voters' questions, announced a Skype conversation with Canadian Prime Minister Justin Trudeau on her Instagram page, and had members of Fat Freddy's Drop play on Parliament's forecourt on her first day as PM.

Ardern has focused on environmental policies since becoming leader, using her party conference address to call climate change this generation's nuclear free moment. How to build its support in 2020 while being part of an Ardern-led Government is now the sizeable challenge facing the Greens.

Former Green MP Keith Locke said with Labour and the Greens overlapping on environmental and child poverty policy, there was a chance to present a clear difference in other areas such as foreign affairs, defence and intelligence services, and how to address New Zealand's booming prison populations.

"I anticipate that Winston Peters will be reasonably conservative in his role [as Foreign Affairs Minister] and Ron Mark in the Defence role."

The Greens had to also get across that they were at the cutting edge in areas like climate change, Locke said, particularly in areas that Labour is still wary of moving strongly on such as banning deep sea oil drilling and reliance on fossil fuels.

"The challenge for the Greens is to show they are the pioneering force."

Locke said with half of the Greens' eight MPs holding ministerial or under-secretary roles it would be difficult to cover all bases and make sure most select committees were covered.

Another challenge would be how to criticise the Labour-NZ First Government. Being ministers outside Cabinet will provide more room, Locke said - but the tone would be crucial.

"I thought sometimes [Act leader] David Seymour's criticisms of National, the tone was a little sharp. It was right from his political perspective to make those criticisms, but possibly he could have made them in a different way."

Seymour was strongly critical of National's record on housing, crime and Resource Management Act reforms, and in the lead-in to the election said the party had abandoned its record of protecting property rights to instead toady up to Peters in order to keep ministerial cars and salaries.

Shaw - who will be joined by a new co-leader, possibly elected before the AGM in June - said the party would look closely at Act's example during its regular post-election review of the good, bad and ugly of its own campaign.

"We will be looking at the Maori Party example, and others through the history of MMP as well and say, 'Well, what did they do well, and what did they do that didn't work as well as perhaps they would have liked?'"

The party was particularly mindful of the "trail" of smaller parties that had previously entered into Government, "and not quite made it out the other side in one piece", Shaw said.

"We are going to have to communicate our wins much more effectively."