When announcing the funding package in May, Health Minister David Clark said in 2017, more than half a million people didn't go to their local GP because of the cost.
"In a country like ours, that's a disgrace," he said.
The policy also extends free GP visits to under-14-year-olds.
Ardern said this was a "big step towards" making New Zealand the best country in the world to be a child.
NZ First's Health spokeswoman Jenny Marcroft said she was excited to see this policy become a reality.
"The implementation of the under-14s policy was a key commitment in the Labour/NZ First Coalition agreement."
The policy would see an additional 56,000 young people eligible for free doctor's visits.
Clark said so far more than 80 per cent of GPs have signed up to deliver cheaper visits for their patients.
"Not only will cheaper doctors' visits mean more people will be able to afford to get the care they need, that will mean many health issues can be identified and treated early before they become major problems requiring hospital treatment."