Douglas Carswell said Britain's vote to leave the EU made it the right time to leave the party, adding that he did so "amicably".
Writing on his website, Mr Carswell said it was a "job done" on Brexit, and he would now focus on constituency issues.
He said: "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.
"I will leave UKIP amicably, cheerfully and in the knowledge that we won."
Although the loss of its only representative in Parliament will be seen as a blow by some, there are many within UKIP who will be glad to see the back of him.
Since defecting from the Conservatives to UKIP in 2014 Mr Carswell's relationship with senior party figures, including former leader Nigel Farage and millionaire donor Aaron Banks, has turned irretrievably sour.
Mr Carswell repeatedly called for Mr Farage to step down as leader during his tenure, with the latter calling the MP "irrelevant".
Douglas Carswell has quit UKIP
Both Mr Farage and Mr Banks have accused Mr Carswell of trying to destroy the party from within, to the point Mr Banks has even suggested he will stand against Clacton's sitting MP in the next general election.
THe bitter public feud reached fever pitch last onth when it was suggested Mr Carswell had attempted to thwart Mr Farage being awarded a knighthood.
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Mr Farage responded by writing a highly critical piece in the Telegraph, calling for Mr Carswell to quit UKIP.
"As a party, how can we let a man represent us in the House of Commons who actively and transparently seeks to damage us?," Mr Farage wrote.
“I think there is little future for Ukip with him staying inside this party. The time for him to go is now."
Moments ago, the Leave.EU campaign, which Mr Banks founded, tweeted a poll asking if Mr Carswell was a "Tory plant" all along.
The tweet read: "Duplicitous Douglas Carswell, who supports mass immigration, is finally out of UKIP. Was he a Tory plant all along?"
And a UKIP source told the Express: "Champagne corks are popping."
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
Duplicitous Douglas Carswell, who supports mass immigration, is finally out of UKIP. Was he a Tory plant all along?
— LEAVE.EU (@LeaveEUOfficial) March 25, 2017
Carswell has ben involved in a long-running feud with former UKIP leader Nigel Farage
Bill Etheridge, UKIP MEP for th West Midlands, said he was "delighted".
"It's a lovely, sunny day and someone I believe was not genuinely interested in representing UKIP in Westminster but has been the focus of serious infighting in the party has gone," he said.
"But I think he needs to step down and call a by election: he might think he can get away with not doing so because he is becoming an independent but I no more believe that than I do the moon is made of cheese.
"He was elected twice on a UKIP ticket, with UKIP resources and the hard work and shoe leather of UKIP activists."
Carswell and Farage together in 2014, before their friendship turned frosty
Mr Carswell has been an MP since 2005, first for Harwich and then for the newly-created constituency of Clacton, in Essex, since 2010.
He had long campaigned for Britian to leave the EU, and threw then Prime Minister David Cameron's election plans inot disarray when he quit the party and called a byelection.
He was ther first MP since 1982 to resign their seat and fight the resulting byelection for an opposing party.
After winning the byelection, he became UKIPs first ever member of Parliament, joined later that year by Mark Reckless, who won the byelection in Rochester and Strood.
Mr Reckless was defeated in the 2015 general election, leaving Mr Carswell as UKIP's only MP once more.