A victorious Labour Party caucus will meet this afternoon to elect cabinet ministers to serve in Prime Minister-elect Jacinda Ardern's coalition government with New Zealand First.
New Zealand First leader Winston Peters' announcement last night of his party's coalition choice sees Labour back in government after nine years in opposition.
The Greens have also announced they are backing Labour on a confidence and supply basis, giving the combined parties 63 seats, two more than the 61 majority they need.
"I am confident the agreement reached with Labour will deliver the most green change of any Government in New Zealand’s history," said leader James Shaw.
"We have spent nearly 30 years working towards being part of Government to deliver change for our people and our environment.
"It's the first time the Green Party will hold ministerial positions to deliver real change that benefits our country."
Mr Shaw went on to say "the hard work starts now and the Green Party is raring to go".
New Zealand First will have four cabinet positions and one parliamentary undersecretary role, Ms Ardern confirmed.
Mr Peters has been offered the position of deputy Prime Minister, pushing aside Labour's deputy Kelvin Davis, but is yet to decide if he will take up the role.
"Early next week we will be in a position to sign and release the agreements that Labour has negotiated both with New Zealand First and with the Green Party," Ms Ardern said last night.
"Later in the week we will confirm and release ministerial portfolios more broadly and a swearing in ceremony will take place."
Ms Ardern, who only found out the news of NZ First's decision at the same time as the rest of the country, opened her first press conference as Prime Minister-elect by acknowledging her predecessor in the role, National leader Bill English.
"I want to thank Bill English for the role he has played in this campaign but also as prime minister and as serving in the past as NZ's finance minister," she said.
"Mr English has already called me this evening and acknowledged that negotiations for the National Party have now concluded."
The congratulatory calls started rolling in soon after NZ First's announcement, though Ms Ardern missed a call from Australia's opposition leader Bill Shorten.
Ms Ardern said she expected to make a trip to Australia as soon as possible, given Foreign Minister Julie Bishop's concerns around working with a Labour government.
She is also anticipating attending the APEC Summit in Vietnam next month.
Mr Peters said NZ First made the decision based on how to best mitigate, not worsen, what New Zealand is expected to face in the coming years.
He has anticipated an economic correction or slowdown and believes the major policies secured in the negotiations are the best to advance New Zealand's economic and social condition.
"Big or small, all of these policies are important," he said.
"It is not my privilege or responsibility to summarise and announce them today, that will befall someone else."
Ms Ardern said Labour remains committed to its Kiwibuild policy to build houses.
She also said all parties agreed that New Zealand rivers are dying and that they've found a path forward to take action on this.