Carswell was originally elected in Clacton as a Conservative party MP, 2010, but defected to UKIP, 2014, forcing a by-election which he won with a substantial majority of 12,404 votes. He was re-elected in 2015 at the general election, but had often crossed swords with Nigel Farage, the UKIP party's former leader.
"It has been an extraordinary achievement. UKIP, my party, which was founded in 1993 in order to get Britain out of the European Union, has now achieved what we were established to do," Carswell wrote on his blog.
Carswell has jumped before he was pushed. He was never UKIP and sought to undermine us. He should have gone some time ago.— Nigel Farage (@Nigel_Farage) March 25, 2017
"On Wednesday [March 29], the Prime Minister is going to trigger Article 50, beginning the formal process of withdrawing our country from the EU. By April 2019, Britain will no longer be a member of the EU. After twenty-four years, we have done it. Brexit is in good hands.
"UKIP might not have managed to win many seats in Parliament, but in a way we are the most successful political party in Britain ever. We have achieved what we were established to do — and in doing so we have changed the course of our country's history for the better. Make no mistake; we would not be leaving the EU if it was not for UKIP — and for those remarkable people who founded, supported and sustained our party over that period," he wrote.
Carswell inferred that UKIP had done its job — in getting Britain out of the EU — and that he no longer wished to be associated with it.
"Like many of you, I switched to UKIP because I desperately wanted us to leave the EU. Now we can be certain that that is going to happen, I have decided that I will be leaving UKIP.
"I will not be switching parties, nor crossing the floor to the Conservatives, so do not need to call a by election, as I did when switching from the Conservatives to UKIP. I will simply be the Member of Parliament for Clacton, sitting as an independent," he added.
UKIP party leader Paul Nuttall denounced Carswell, saying: "When he has spoken about the need for more 'grown-ups' in politics, I had hoped he would do more to lead by example"
"Over the last year it has become clear that he has been drifting in one direction while UKIP has been marching in another. He has always been and always will be at heart a Brexit supporting staunch Tory, and with the referendum result sorted he has no reason to stay in a party that is moving into Labour's turf rather than going in a direction that would make him feel more at home," Nuttall said.