Up to half a million special votes - including overseas votes from Australia - will be counted in the next fortnight but are not expected to substantially change results.
Ms Ardern must now decide whether to keep governing with the Greens, growing her coalition, or use the mandate conferred by Kiwis in a record vote to go it alone.
"I want to talk with the Greens and we'll do that next week," she said in Auckland on Sunday.
"But that mandate does exist for Labour."
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Unlike Australia, coalition governments are the norm in New Zealand.
After elections, major parties spend weeks in negotiations with minor parties, courting their support to form a government.
It was how Ms Ardern came to power in 2017, when the Greens and populist outfit New Zealand First both pledged to support Labour rather than the National party, which won the highest party vote.
This time however, the shoe is on the other foot.
It is Ms Ardern who can choose whether to invite the Greens in, or not, and she will seek the input of her newly-bolstered caucus in a party meeting on Tuesday.
Grant Robertson, finance minister and Ms Ardern's closest political ally, suggested Labour was well disposed to another coalition.
"Jacinda Ardern's leadership style is one to build consensus. We'll look to do that but we sought a very strong mandate for Labour and we got that," he told TVNZ.
Across town, the Greens were celebrating their own success.
Minor parties that go into government are often decimated by taking that decision.
The left-wingers are the first party to increase their vote share after doing so.
In 2017, they polled 6.3 per cent of the vote, and after 96 per cent of the party vote in the 2020 poll, they were up to 7.5 per cent.
More impressively, political wunderkind Chloe Swarbrick has pulled off a major coup, winning Auckland Central against the might of the major parties.
Co-leader James Shaw said he was "absolutely stoked" by the result, with his fellow co-leader Marama Davidson saying her "feet were a little bit off the ground. It's an incredible night".
On stage at his party function, Mr Shaw was elated.
"We're still here! We are beyond thrilled to be able to say 'we did it'."
Ms Ardern has other decisions to make too, including a new foreign minister after the defeat of Winston Peters' New Zealand First.
NZ First was the third of three parties in the Labour-led government, but will not be returned to parliament after missing the five per cent threshold.
Final election results, after the counting of the special votes, as well as the result on referenda to legalise cannabis and euthanasia will be known in two weeks.