Prime Minister Jacinda Ardern and Children's Minister Tracey Martin announced the policy at Kaitao Intermediate School in Rotorua on Thursday.
It's part of the Government's Child and Youth Wellbeing Strategy.
Ardern said the idea behind the free lunches policy was "pure and simple – Do we want our kids to go hungry?"
The obvious answer, she said, was no.
"That's why the Government is rolling this school lunch programme out to the kids in New Zealand who need our support the most."
She added that the lunch in schools programme would contribute to the Government's pledge to reduce child poverty.
"You simply can't learn distracted by an empty stomach."
The Government consulted with children across the country before it launched the Wellbeing Strategy, Ardern said.
"Children themselves told us during the consultation on the strategy that going to school hungry was a barrier to their learning.
"That was heartbreaking to hear and this prototype starts to ensure children are fed and have the best chance to succeed."
The free school lunches programme is one of 75 initiatives the Government unveiled today.
The wellbeing strategy aims to reduce child poverty, better support children and young people in care addressing family and sexual violence and put more focus on mental wellbeing.
Kaitao Intermediate's school hall was packed for Prime Minister Jacinda Ardern's announcement.
School pupils as well as Rotorua Lakes Council representatives, Te Arawa leaders, local principals, Government staff and Children's Commissioner Judge Andrew Becroft were there. Becroft applauded the strategy.
"This is a co-ordinated, integrated plan for the first time. Properly implemented it could be a game-changer.
"Ten per cent [of children] are in chronic disadvantage. This is not the New Zealand we should be proud of, this is not the New Zealand that we want ... and for the first time we've confronted it as a country.
"We're better than this. As a country, we deserve to do better for our children. Children have told us what they want, we know what they need, this is their right and this delivers on it."
He said he hoped free school lunches for all New Zealand children would be the long-term goal.