A soldier guarding the meeting room containing Churchill, US President Dwight Eisenhower and French Premier Joseph Laniel collected the still-smoking cigar when he was sent in to tidy up afterwards.
Welshman Sergeant Rudolph Hughes stubbed it out in an ashtray before pocketing it as a souvenir.
The La Aroma de Cuba cigar, which Churchill was known to smoke alongside his more famous Romeo y Julieta brand, is about three-and-a-half inches long.
The cigar is being sold with a letter of provenance from the soldier who was serving with 1st Battalion Royal Welsh Fusiliers in Jamaica when he was sent to Hamilton, Bermuda, in 1953 to guard some of the world’s most important men of the time.
Sgt Hughes stood outside the main conference room for several hours, armed with a machine gun, alongside two FBI men.
His letter reads: “The conference lasted several hours.
“When over, and the conference room emptied, Capt Sinnet and myself and others, went in for souvenirs.
“Capt Sinnet took small flags of each country involved.
Myself, I took Winston Churchill’s still smoking cigar from his ashtray, stubbed it out, and have kept it for 50 years.”
The cigar was acquired by an anonymous private collector about 10 years ago and they have now made it available for sale at auction. A CIGAR half-smoked by Winston Churchill during a Cold War conference with world leaders is going up for sale.
As well as the letter of provenance, the cigar also comes with various Bermudian press cuttings and Sgt Hughes’ Bermudian driving license.
The Bermuda three-power conference was held from December 4 to 7, 1953, to discuss relations with the Soviet Union, atomic energy and Egypt.
It was arguably the most powerful gathering of world leaders since the Potsdam conference in 1945, when the US, UK and USSR heads of state met to decide how to punish Nazi war criminals.
The auction is being held by PFC Auctions in Bristol and the cigar is expected to sell for £3,000.
Adrian Roose, from PFC Auctions, said: “It’s rare to see a half-smoked Churchill cigar at auction.
“Unused cigars sell for a few hundred pounds, but collectors love half smoked ones, knowing that Churchill actually puffed away on it is a huge deal.
“Provenance is everything with items like this, otherwise it’s just hearsay.
“This provenance comes directly from the soldier guarding the meeting room, it doesn’t get much better.
“When we think of an image of Churchill, the cigar isn’t far away.
“It’ll make a great display piece and great dinner party conversation, regardless of who purchases it – museums, collectors, or just someone interested in buying a small piece of Winston Churchill history.
“He is consistently voted the greatest Briton of all time.
“He is an iconic figure and from a collecting point of view there really isn’t that much Churchill memorabilia available.
“There’s the odd letter and signature, but personal items, like his dentures, his spectacles, his half smoked cigars, they’re the items collectors fight over.”