Prime Minister Jacinda Ardern says Simon Bridges brings a new generation of leadership to the National Party but she's "absolutely" sure she can beat him in 2020.

"I will treat him as I would any new leader of the National Party," she said on Tuesday.

"We have robust exchanges, all of us, and I expect it will continue."

The Greens congratulated Mr Bridges.

"He has an opportunity to redefine his party for the future," said co-leader James Shaw.

"I hope that he takes this opportunity to work constructively across the House on the most important challenges we face together as a country."

ACT leader David Seymour said that under Mr Bridges, National would need the ACT Party even more.

"Voters on the right who value personal freedom will be concerned about his socially conservative views," Mr Seymour said.

"Whereas John Key votes for marriage equality and pledged to vote for the End of Life Choice Bill, Mr Bridges voted against both."