Muller said by announcing today he hoped to give the National Party and local branches "ample time to find their next candidate".
"The National Party needs to take the opportunity this term to renew and refresh, with strong new candidates lining up for the next election.
"The highlight of my role is undoubtedly serving my local community.
Judith Collins and Todd Muller on June 4. Photo / George Novak
"At a national level I am very proud of the work I did with James Shaw in creating bi-partisan support for climate action and achieving cross-party support for the Zero Carbon Act.
"I look forward to working out my term with the National team. In the meantime, I am on pre-approved leave for the next five weeks, to care for my wife who is undergoing a significant medical procedure. I will return to Parliament after the winter recess."
'We thank him for his service' - Collins
National Party leader Judith Collins said Muller had announced his decision to her and the caucus.
"We thank him for his service and we support his decision," she told Newstalk ZB.
Muller had committed to undertake his work until the 2023 election, Collins said. She wouldn't speculate on whether he could retire sooner.
Muller was first elected to Parliament in 2014 as the MP for Bay of Plenty, a seat he won again in 2017.
He was seen as a rising star and future leader of the party.
On May 22 last year, election year, Muller secured the position of leader of the National Party, ousting predecessor and Tauranga MP Simon Bridges in the process.
Just 53 days later, Muller made the shock announcement he was stepping down from the role for health reasons.
