Defence Secretary Ben Wallace has confirmed he will leave Cabinet at the next reshuffle and not seek re-election as an MP.
The announcement follows an unsuccessful bid to replace Jens Stoltenberg as Nato secretary general.
Speculation had grown that he would replace the former Norwegian prime minister as head of the alliance before he revealed in an interview with The Economist that “it’s not going to happen” and there are “lot of unresolved issues” in Nato.
He had been tipped for the post due to his pivotal role in overseeing the approach the UK and many of its allies took in response to the Russian invasion of Ukraine last year.
Here the PA news agency looks back at his life in politics.
Born in 1970, the 53-year old trained as a cadet at Sandhurst military academy before rising through the Army’s ranks to become a captain in the Scots Guards.
Upon leaving the Army he entered politics, joining the Scottish Parliament in 1999 as a Conservative at the party’s lowest ebb north of the border.
He did not seek re-election to Hollyrood in 2003 and won the Lancaster and Wyre Westminster seat south of the border off Labour in 2005.
Five years later, the constituency was abolished and he moved to the safer Wyre and Preston North seat.
He served in various junior ministerial roles under David Cameron and became an early supporter of any future bid by Boris Johnson for the Conservative leadership.
Unlike the ex-PM, he backed Remain in the 2016 referendum but nonetheless ran Mr Johnson’s subsequent leadership campaign.
He did not reach Cabinet until Mr Johnson succeeded Theresa May, under whom he had been security minister, and promoted him to Defence Secretary.
He has remained in post since despite two Conservative leadership contests, three Prime Ministers and party infighting.
In his post he has co-ordinated the UK’s response to the US withdrawal from Afghanistan and later the Ukraine war.
During an LBC radio interview he broke down in tears as he said he felt emotional “because I’m a soldier” and added “some won’t get back” from the country.
He met Russian defence minister Sergei Shoigu in early February last year for last minute talks as tensions with Ukraine rose, concluding the following day that an invasion was “highly likely.”
Since Russian tanks rolled into Ukraine, he has played a key role in shaping the Government’s response, including helping determine what weapons the UK will send to Kyiv.
Despite drawing praise and being tipped as the activists’ favourite, he nonetheless ruled himself out of contests to succeed Boris Johnson and Liz Truss.
Speculation mounted in recent months that he would become the next Nato secretary general until he said the US would prefer Mr Stoltenberg to remain in post for another year.
Mr Wallace also said he is unlikely to run for the position again if it comes up in future.
Despite escaping relatively unscathed from many of the controversies that have plagued PMs he has served under, he has occasionally found himself in hot water over the odd off-script remark.
In March last year, video emerged of him on a Teams call with Russian “pranksters” believed to have links to the country’s intelligence agencies, who posed as the Ukrainian prime minister, Denys Shmyhal.
The call was said to have lasted about 10 minutes and he is not believed to have disclosed anything sensitive.
At a Nato summit last week, he appeared to suggest Ukraine should show “gratitude” for the military support it has received.
The comments were immediately shut down by Prime Minister Rishi Sunak.
Sources close to the Defence Secretary later said: “Mr Wallace was reflecting on the need for Ukraine to address the parts of public opinion and parliaments in the international community who need to be encouraged.”
