Rory Stewart quit the Tory party to stand as an independent in London Mayor race.
He announced he was standing down as the MP for Penrith and The Border at the next election.
And in a further shock revelation he said he would be throwing his hat into the ring for the mayoralty.
On his campaign website, he wrote: "I am running as an independent candidate to be Mayor of London.
"This is the most extraordinary city on Earth - but London is also facing one of the most challenging times in its history - we are going to have to work ever more closely together.
"So over the coming weeks and months I will be walking around London – not campaigning, but listening and learning from you about how we can transform this great city together."
Following his announcement Ladbrookes installed Stewart at 4/1 in the betting.
Sadiq Khan is odds-on at 4/6 to remain in his post. Lib Dem runner Siobhan Benita is fancied at 6/1, with Shaun Bailey at 10/1.
Earlier this morning he announced his plans to quit Westminster.
He said in a tweet: "It’s been a great privilege to serve Penrith and The Border for the last ten years, so it is with sadness that I am announcing that I will be standing down at the next election, and that I have also resigned from the Conservative Party."
The announcement was met with regret from many current and former Tory MPs.
Financial Secretary to the Treasury Jesse Norman described it as a "terrible pity".
He said Rory Stewart is "both wildly talented and a wonderfully decent human being".
Writing in The Cumberland and Westmorland Herald, he explained that he would not be standing as an independent in the same seat.
He told constituents: "As you will be aware, I am no longer allowed to run as Conservative MP in Penrith and The Border.
"Because I have loved the constituency so much, I had considered standing as an Independent; but I have decided that I wouldn’t want to run against those Conservative members who have been such wonderful colleagues over the last ten years."
Speaking about his next steps, he said: "As for the future – I am a public servant to my core and will stay involved in politics, endeavouring to make my voice heard."
Hinting at his move to London, he said: "I hope to start work in another part of the country."
Mr Stewart's departure follows similar announcements by colleagues from the more moderate wing of the Conservative Party.
