Opposition leader Chris Luxon made the categorical statement on Wednesday, ending months of speculation.
"The bridge between National and Te Pati Maori is too wide to close," he said.
The announcement is important as in NZ politics, the formation of governments depends on coalition talks following each general election.
The electoral system makes it incredibly difficult for any one party to achieve a majority, though Jacinda Ardern's Labour did so in 2020.
Polls suggest the election is tipped to be incredibly close, with current government partners Labour and the Greens matching up almost identically to National and its likely government partner, the right-wing ACT party.
The Maori Party, the fifth and smallest party in parliament, was a possible kingmaker until Mr Luxon's declaration.
While it is left-wing, the party supported John Key's National-led governments.
Mr Luxon said he considered the current iteration of the Maori Party too radical to govern with.
"Te Pāti Māori of 2023 is a very different party to the one National signed a confidence and supply agreement with three times from 2008," he said.
The decision cuts off a potential road to power for Mr Luxon's National, but frees them to attack the party, which it has labelled "separatist", and by association, Labour.
It has already begun to do so in the wake of Labour minister Meka Whaitiri's defection to the Maori Party last week, running attack ads accusing them of being one bloc.
"A vote for Te Pati Maori is a vote for the Labour/Greens/Maori Party coalition of chaos and continued economic mismanagement," he said.
"National is deeply committed to improving outcomes for Maori, but doesn't believe separate systems is the best way to do this.
"We believe New Zealand is one country with one standard of citizenship, meaning one person, one vote.
"National will campaign hard for every party vote in the election this year so we can become the stable government that New Zealand needs."
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