The first Matariki public holiday will be on June 24, in 2022, the Prime Minister has announced.
Jacinda Ardern announced the first date today, and said it would move around in following years to fit in with the rising of Matariki - a cluster of stars that rises mid-year and marks the Māori New Year.
A new panel of experts on tikanga and astronomy would set the dates for future years – but it is likely to always be on a Friday or a Monday.
Matariki marks the rising of the cluster of stars known as the Pleiades. It usually rises in late May or early June. In Māori tradition it is seen as a time of renewal.
Ardern said it was time to have a distinctly New Zealand holiday: "a time for reflection and celebration, and our first public holiday that recognises Te Ao Māori".
"This will be a day to acknowledge our nation's unique, shared identity, and the importance of tikanga Māori. It's going to be something very special, and something uniquely New Zealand.
"It will also break up the lag between public holidays that currently exists between Queen's Birthday in early June and Labour Day in late October."
The new public holiday was one of Ardern's first campaign promises in September last year.
It will be the first new public holiday in New Zealand in almost 50 years and the 12th public holiday of the year.
A new Matariki Advisory Group would include Professor Rangiānehu Matamua (chair), Hoturoa Barclay-Kerr, Rereata Makiha, Victoria Campbell, Dr Pauline Harris, Dr Ruakere Hond, and Jack Thatcher.
"This group will ensure that Mātauranga Māori is at the forefront of decision-making about the public holiday. Each of the members are recognised experts in Te Ao Māori and mātauranga associated with Matariki and the Maramataka," Māori-Crown Relations Minister Kelvin Davis said.
The group is expected to start to work out the dates of the holiday for the next 30 years, to give businesses certainty about when it would happen.
Matamua said different iwi marked the occasion in different ways "so it's important this holiday acknowledges those regional differences".
Workplace Relations Minister Michael Wood said it would give tourism businesses in particular something unique to market to international visitors, once borders re-opened.
There had long been calls for a holiday to mark the significant event in the Māori calendar, especially given the country had public holidays for Queen's Birthday and religious days of Easter and Christmas.
A petition by Laura O'Connell Rapira raised more than 35,000 signatures last year.
However, Labour's announcement in September was not universally welcomed: while the Green Party supported it, NZ First, National and Act all questioned whether there was a need for another public holiday.
National had suggested it should replace another public holiday rather than add a further one, saying it would put more pressure on businesses at a difficult economic time.