Former UKIP MP Douglas Carswell has announced he will not stand in the general election.
Mr Carswell said he would be voting Conservative on June 8 but has decided that "it is time for me to move on to other things".
The Clacton MP sensationally defected from the Tories to UKIP in 2014 and became the eurosceptic party's first elected MP in a subsequent by-election.
I look forward to being able to read newspapers without appearing in them" - Douglas Carswell
But he fell out spectacularly with then leader Nigel Farage and quit UKIP earlier this year to sit as an independent.
He was facing a potential challenge in the upcoming election from millionaire businessman and former Ukip funder Arron Banks, who accused him of deliberately undermining the party and Mr Farage.
In a message to constituents, Mr Carswell said: "I have done everything possible to ensure we got, and won, a referendum to leave the European Union, even changing parties and triggering a by-election to help nudge things along.
"Last summer, we won that referendum. Britain is going to become a sovereign country again.
"I have decided that I will not now be seeking re-election.
"I intend to vote Conservative on June 8 and will be offering my full support to whoever the Clacton constituency Conservatives select as their candidate.
"It is sometimes said that all political careers end in failure. It doesn't feel like that to me today.
"I have stood for Parliament five times, won four times, and helped win the referendum last June. Job done. I'm delighted.
"Having been an MP for about half my adult life, I believe that it is time for me to move on to other things.
"I look forward to being able to read newspapers without appearing in them."
Mr Carswell, 45, was first elected Conservative MP for Harwich in 2005 and has represented Clacton in Parliament since 2010 following boundary changes.
He had a solid 12,000 majority as a Conservative in the 2010 election, holding the seat by almost 3,500 votes for UKIP in 2015.
Liberal Democrat foreign affairs spokesman Tom Brake said: "This is yet another top Brexiteer leaving a sinking ship.
"After steering the country towards a disastrous hard Brexit, it seems leading Leave campaigners don't want to be held accountable for what happens next.
"It also speaks volumes that Ukip's first elected MP is throwing his weight behind Theresa May, who has adopted UKIP's hard Brexit agenda to the letter."