The Prime Minister says he would have liked cabinet minister Tony Ryall to stay on after the election but understands his decision to retire.
The Bay of Plenty MP, who has been in Parliament since 1990, on Thursday made a surprise announcement that he will quit politics at the election later this year.
Mr Ryall, 49, will keep his portfolios of health and state-owned enterprises until the election.
John Key said Mr Ryall has been an amazing Health Minister but the reality is that he has been an MP for 24 years and is looking to have a career outside Parliament.
Mr Ryall, who's the 14th National MP to say they will not stand for re-election this year, said this was the right year for him to leave politics and he's "looking forward to being part of New Zealand's dynamic future in the private sector".
"I came to Parliament as a young man - I think I'm still a young man - and I think this is the right time for me, and also the right time for my family, the electorate and the country."
He said he had discussed his decision with Mr Key and Deputy Prime Minister Bill English, who were disappointed but supportive.
Mr Ryall entered Parliament as National MP for East Cape at the age of 26 and became a cabinet minister in the National-led government between 1997 and 1999.
He has held his current portfolios since the current National-led government was elected in 2008. His majority in the Bay of Plenty electorate is 17,760.
A legacy 'very few will match'
National Party president Peter Goodfellow says Mr Ryall has made an outstanding contribution as a politician and will leave a legacy that very few will match.
But the Labour Party says he leaves a negative legacy on state assets, with partial sales and the collapse of Solid Energy.
The Green Party says he has only focussed on short-term gains and still has questions to answer about a case of potential fraud involving Southland DHB money.