National MP and former Health Minister Jonathan Coleman has called time on Parliament, sparking a by-election in his Auckland seat.

Coleman, the MP for the safe National electorate of Northcote, announced on Thursday he was resigning from politics and was expected to make his valedictory speech in the next couple of weeks.

The party's number six has been offered a significant opportunity to run a private sector health company Acurity, which owns Bowen, Royston and Wakefield private Hospitals.

"To be honest, it was a pretty tough decision. I thought about it long and hard. But in the end, it's a personal decision that I've made in terms of looking to the next phase of my career and what is going to be best for my family."

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His resignation comes only a couple of weeks after his colleague, Steven Joyce, also decided Opposition politics wasn't for him.

Coleman came into Parliament in 2005 and under the National-led government held ministerial portfolios including, state services, defence and sport and recreation.

FAIRFAX NZ Former Health Minister Jonathan Coleman got promoted up one place on the front bench in National Party leader Simon Bridges' reshuffle but he's decided to call time on politics.

In 2014 he became the first doctor in 70 years to hold the health portfolio.

"It's been a huge privilege to serve as a Member of Parliament for the past 13 years, nine of them as a Cabinet Minister. I have greatly enjoyed my time as a Member of Parliament, and am proud of the work I've been involved in, both as a Minister and as the MP for Northcote.

"I especially wish to thank the people of the Northcote electorate for their support over those years," he said.

"I also feel fortunate to have had a long and stimulating career as a Minister and to have worked closely with two great prime ministers in Sir John Key and Bill English.

"I was not looking to leave Parliament, but received an unsolicited approach from Acurity. It's a very exciting opportunity that utilises my skills and draws on my background both outside and inside Parliament," Coleman said.

He said he informed party leader Simon Bridges yesterday of his decision, but the pair had not discussed any potential replacements for him in the health portfolio.

There were any number of capable candidates within the party, he said.

Mark Tantrum Dr Jonathan Coleman performs an ear examination on patient Tana Petimanu (11) at Karori Medical Centre on July 1, 2015 in Wellington, New Zealand. Coleman had just announced plans for free prescriptions and visits to GP's for children under 13 years of age.

THE NORTHCOTE BY-ELECTION

Coleman said National was "well placed to win" the Northcote electorate again, but it was one no candidate should take for granted.

"It's a seat I've held for five elections, it is a seat where people have supported National over many years," he said.

Coleman rejected suggestions he was doing his electorate a "disservice" by triggering a by-election so soon after a general election.

"I've given 13 years of public service as the MP for Northcote and I've been out to talk to some of my constituents about this and I've actually had overwhelmingly positive feedback.

Unknown Health Minister Jonathan Coleman and Prime Minister Bill English #twinning at work.

"By-elections are a fact of life, both Labour and National have had them over the years and you get up to two three every cycle," he said.

"But it's also a great opportunity that National is in this phase coming out of Government, for some exciting new talent to come onto the stage and a great opportunity for Simon Bridges to come out and meet the people of New Zealand.

"And my view has always been that it's best to go, not only while you're still enjoying it, but while people want you there."

Coleman holds a 6200-vote majority in the electorate. He's held it by more than 10,000 votes in the past, but said the rising popularity of Labour at the last election was reflected in their electorate vote.

He had not had any conversations over potential candidate replacements for him, but said it was a matter for the party.

A VARIED CAREER

Coleman said his political career had given him opportunities he had been "incredibly grateful" for, but it was time bow out.

"It is clear to me that it is the right time to embrace this unique offer as I look to a future beyond politics."

He said he wanted to "acknowledge and thank leader Simon Bridges and wish him and my caucus colleagues well on their path back to the Treasury benches".

Bridges thanked Coleman for "many years of dedication and service".

"Jonathan has had a long and distinguished career in politics, including 13 years as MP for Northcote and nine as a minister.

"He has been a diligent and committed colleague who has handled a range of challenging portfolios with a focus on getting results. As Immigration Minister he focussed policy on importing skills and capital while fundamentally reconfiguring the immigration network," he said.

"As State Services Minister he oversaw legislation that implemented the biggest changes to public service operation in a generation.

"During his time as Defence Minister, New Zealand's defence relationship with the US continued to grow closer and Dr Coleman oversaw the withdrawal of New Zealand troops from three major deployments - Afghanistan, Timor Leste and the Solomon Islands. At the same time he drove the reconfiguration of NZDF to support New Zealand's future foreign policy intentions."

Bridges acknowledged Coleman's work as Associate Finance Minister - "involved in the delivery of three very successful Budgets".

KIRK HARGREAVES/STUFF Jonathan Coleman has a hit at Hagley Oval ahead of the 2015 ICC Cricket World Cup.

"And finally as Health Minister, Dr Coleman initiated and drove the New Zealand Health Strategy - the blueprint for the future of New Zealand health services - while delivering a continued increase in access to clinical services across the board.

"My colleagues and I wish Jonathan and his family the very best for this new phase of their lives," he said.

"I am confident that the new National Party candidate will show they have a real understanding of that community's aspirations and a commitment to working with local people to achieve them."

Coleman made his leadership ambitions in the National Party known when he put his hat in the ring for leader when former-prime minister Key resigned in 2016.

He withdrew in the eleventh hour when it became clear the numbers had stacked in the favour of English - Key's deputy.

ANTHONY AU-YEUNG Sport and Recreation Minister Jonathan Coleman shakes hand with Peter Burling, helmsman of Team New Zealand during the Team New Zealand Americas Cup Welcome Home Parade on July 6, 2017 in Auckland.

Coleman was tipped to run again for the leadership when English announced he was leaving politics earlier this year.

However he never joined the race, which ended up with five contenders, and when Bridges announced his reshuffle Coleman was promoted to number six on the list - up from seven - and retained his health and sport and recreation portfolios.

It's understood Coleman was lining himself up for the finance role and was disappointed after the reshuffle, prompting his decision to look for other opportunities.

DENISE PIPER/STUFF Former Ministers: Seniors minister and North Shore MP Maggie Barry, Health Minister and Northcote MP Jonathan Coleman and Prime Minister Bill English speak with Liz Godfrey, from Birkenhead, as she recovers from a partial knee replacement at North Shore Hospital.

Coleman confirmed however, Acurity had approached him with the offer during the leadership contest and he had already made the decision not to run for leader again before English announced his retirement.

Coleman had a chequered record in the health portfolio; during his three years in the role he faced intense pressure over healthcare funding and staffing shortages.

The leadership at the Ministry of Health came under huge fire during his time and he was heavily criticised for the Government's response to mental health issues across the country and a lack of funding.

But he also oversaw the implementation of the New Zealand Health Strategy - the first updated blueprint for the health sector since 2000 - and the signing of a historic equal pay agreement with union champion Kristine Bartlett that gave pay equity to about 55,000 of her low paid, mainly female colleagues in the aged care sector.

He oversaw a massive increase in the number of elective surgeries being performed in the public health system, from 56,000 to 174,000 during the time National was in power. But one thing he said he regretted not having the chance to do was to implement the social investment policies the party was working on with regards to mental health.

Coleman had not settled on an official resignation date yet, but it would be within the current sitting block that he would be delivering his valedictory speech. It was up to the prime minister to call for a by-election in Northcote after his formal resignation.

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