The memorial will be broadcast and livestreamed so all New Zealanders could take part, she said.
There will also be two large screens at Parliament grounds for people to watch it on.
Invited guests at the service in Wellington will include representatives from a broad range of New Zealand communities and from organisations with particular links with the Queen, Ardern said.
The Queen came to New Zealand 10 times and visited 46 cities and towns.
"We know in communities across the country, people will want to show their respects to a monarch who dedicated her life to service," Ardern said.
"She will continue to hold a special place in the hearts of many."
Acting Prime Minister Grant Robertson is fronting a press conference following today's Cabinet meeting.
MBIE has confirmed that standard public holiday requirements under the Holidays Act will apply and there will be no shop trading restrictions or restrictions on the sale of liquor.
Some have criticised the move given the expense and wider impact on the economy and society.
New Zealand is following suit with the UK and Australia, which have announced similar holidays of their own.
The new sovereign, King Charles III, has announced the Queen's funeral today (from 10pm NZ time) would be a bank holiday in the UK. Australian Prime Minister Anthony Albanese confirmed that September 22 would host their public holiday.
