The Greens say they'll still push for a wealth tax and solving other inequality gaps, despite the specific issues not forming part of their ministerial responsibilities under the new Government deal signed with Labour today.

Prime Minister Jacinda Ardern, deputy Labour leader Kelvin Davis and Green co-leaders James Shaw and Marama Davidson have signed the Labour-Greens cooperation agreement.

Ardern said it was "fantastic" to have the agreement formalised. Shaw called it a "win-win".

Davidson said she could still stand strong - even against the Government - on the Ihumatao issue because that was an issue outside of the Greens' ministerial portfolios.

She also said the party's wealth tax was not part of the ministerial portfolios given to the Greens, so the party could continue to push for ways to address inequality.

The signing took place in the Prime Minister's boardroom on the ninth floor of the Beehive this morning.

Ardern outlined the agreement, saying it represented the continuation of the Labour-Greens relationship and provided stability.

The agreement means the Greens cannot oppose the Government on confidence and supply.

Last night the Green Party members voted to accept a deal with the Labour Party which will see Shaw and Davidson become ministers outside of Cabinet.

Shaw will be the Minister of Climate Change and Associate Minister for the Environment (Biodiversity).

Davidson will become the Minister for the Prevention of Family and Sexual Violence and Associate Minister of Housing (Homelessness).

Ardern said she wanted to bring as much consensus as possible, though the agreement did not require consensus to be formed.

The cooperation agreement was unique in that "we don't have to agree", she said. There were reasons to have consensus but it wasn't necessary, given Labour held a parliamentary majority without the Greens.

She said tomorrow's announcement about Cabinet positions was about balancing existing experience with new talent.

She said there wouldn't be "large-scale deviation" from existing portfolios or the size of the executive.

She has been "mindful" of acute issues such as Covid-19 in deciding the make-up of Cabinet, noting the strict lockdowns announced in the UK, France and Germany.

Shaw and Davidson provided specific expertise that would be used in their ministerial portfolios, she said.

Davidson said the Greens campaigned on climate change, biodiversity and inequality spaces, and the agreement allowed the Greens to "keep pushing" on those issues while also protecting the Greens' independent voice.

She said time was running out on those issues.

Shaw said it was a privilege and an honour to be returned to Parliament with an expanded caucus and with ministerial portfolios. "We are delighted to have a win-win agreement here."

Davidson said she was proud that the Greens' membership supported the agreement; 85 per cent of members supported the agreement, above the needed 75 per cent.

Shaw said he didn't feel gagged by the agreement - "not in the slightest".

The delegates who didn't support the agreement had compared the arrangement to 2017, but Shaw said it was more reasonable to compare it with 2005 and the 2020 agreement was stronger than that one.

Davidson said the party understood that Labour had offered wins to the Greens despite Labour holding a parliamentary majority.

She said she was honoured to continue Green MP Jan Logie's work towards ending family and sexual violence. "I get to be able to work with her and continue on to the next step."

Ardern said Labour would not put the Cannabis Legalisation and Control Bill into the ballot where it could be drawn as a member's bill.

Davidson said putting the bill forward as a Green MP member's bill had not been discussed with caucus.

Ardern said a cross-parliamentary discussion would be needed about having a four-year term, including whether it should be put to a referendum.

Davidson said a unique aspect of the agreement was to allow the Greens to outline where they would want to go "further and faster" than the Government.

Ardern said "good progress" was being made on a quarantine-free travel bubble with Nuie and she expected a deal to be made "soon", though she didn't specify a timeline.

Davis said he was feeling "fine" going into tomorrow's announcements, which would include the deputy prime ministership.

Ardern said she was hopeful to have a legally clear regime for drug-testing at festivals in time for the summer festival season.

Drug testing operates now but in a legally grey area, and NZ First blocked the work last parliamentary term to provide legal clarity.

Ardern said it wasn't about changing the legal status of any of those substances, but about saving lives.

The testing means that festival-goers can check that the substances they have are what they were told they are, and are not laced with anything else.