The Labour Party leader says the cooperation agreement reached with the Greens means the two parties can agree to disagree.
Jacinda Ardern and deputy Kelvin Davis, along with Green Party co-leaders James Shaw and Marama Davidson, have signed a cooperation agreement that gives the Greens ministerial portfolios outside of Cabinet.
Watch a video of the signing here
Shaw will remain as the Minister of Climate Change and will also become an associate minister for the environment. Davidson will hold the new prevention of family and sexual violence portfolio and associate housing.
After the agreement was signed at the Beehive this morning, Shaw called it a "win-win" for both parties.
Ardern said it was a unique arrangement, considering Labour actually had the numbers to work alone.
"What's unique here is that we're both agreeing that we actually don't have to agree," she told reporters at the signing ceremony.
"That means that actually, if we need to get on with things we can, the Green Party can make it clear where they don't agree while we get on with things, but it doesn't stop our ability to work together."
Ardern said securing confidence and supply by making sure the Greens did not vote against Labour, gave "extra surety for us to be able to govern with the mandate that New Zealand has given us...and an opportunity for us to draw on the skills that exist across Parliament".
Greens co-leader Marama Davidson said they needed a super majority of 75 percent from members but ended up getting 85 percent after last night's call.
"So I'm, again really proud that we have a good mandate, because it shows that this is a cooperation agreement that is a win-win for the Greens that doing work with Labour productively as well as protecting our unique Green voice."
Co-leader James Shaw said there was "some anxiety" about the changed Parliament, which he said was understandable.
People were also comparing the deal to that in 2017 when the Greens had five ministerial portfolios, four associates and an under-secretary, he said.
"However, I think the comparable arrangement is actually the 2005 agreement between the Labour government and the Greens then, and this is a stronger deal."
There were "valid" concerns from members about the Greens losing its political identity by signing up with a larger party, acknowledged Davidson.
"If you have a look at Māori Party, New Zealand First for smaller parties historically, it has always been more of a challenge to maintain that unique position.
"And what we're really proud about and what 85 percent of the member delegates voted for was an agreement that is the best of both worlds. That is a win-win situation for the Green Party," she says.
Under the agreement the Greens have to back the government line over decisions made in their portfolios, but are otherwise free to take a different position to Labour.
Davidson said there was also another mechanism that will help the Greens publicly note where there is disagreement, even in their own portfolios.
"For the first time, this agreement allows us to Cabinet note where there is deviation from the Green Party policy where perhaps we might go further and faster."
In the last Parliament the Greens were part of the governing arrangement with Labour and New Zealand First.
How did it feel for Shaw sitting around the table with Winston Peters absent? "It's a new Parliament and it's a new day" was all he would offer.
Also part of the deal is a commitment them to working with other parties on issues that affect democracy, including 2012 Law Commission recommendations relating to the so called 'coat-tailing' provision, and lowering the five percent threshold.
It also referred to electoral finance law and extending the parliamentary term to four years.
Ardern said the latter was likely something that would go to referendum.
"No politician wants to be seen to be feathering their own nest, traditionally it has gone to referendum, and I imagine that would be a most likely scenario. But if you're in good faith going and having conversations with other parties and cross Parliament, then that's what we should in good faith do."
About 85 percent of roughly 150 Green delegates voted in favour of the deal on a lengthy conference call last night.
The delegates were presented the deal following several rounds of talks between Labour and Green leaders that concluded on Thursday.
The agreement includes little policy detail, but a commitment to work together on child poverty, climate change, and the environment.
It also means the Greens can't oppose Labour on confidence and supply matters, but can take their own position on issues outside of ministerial portfolios and areas of co-operation.
Ardern will announce her new Cabinet line-up at Parliament tomorrow.