The spectacular find has been valued at £15,000 (€16.000) by Bristol East Auctions, but pre-auction bids online stand at £50,000 (€55,000)
The early 20th century gold-plated circular-rimmed glasses owned and worn by the civil rights leader were given as a gift to the vendor’s uncle.
Decades later, the rare item was found in the most unusual of circumstances, said auctioneer Andy Stowe.
Speaking to PA news agency, he said: “It was about two, three weeks ago a gentleman who lives fairly locally to us came down on an evening stroll on a Friday night with the glasses.
“We found the glasses hanging halfway out of the letterbox in an envelope with a note saying ‘these glasses belong to Gandhi, give me a call at your earliest convenience’.”
Mr Stowe and his team discovered the glasses were given to the vendor’s uncle while he was working for BP in South Africa between 1910-1932.
“He was known for giving things away quite openly,” Mr Stowe said.
The vendor is in his 80s with no family to pass the glasses on to, Mr Stowe added.
When asked how sure he was the glasses are genuine, he said: “Without Gandhi here to tell us himself that they’re his, we can’t be absolutely sure, but the stories all check out.
“It was the right time and the right place, the glasses are a near identical to the ones we found in a museum.
“Those glasses had a bent bridge that would match the contours of Gandhi’s nose and ours matches that.
“There are only around four or five pairs around the world, Gandhi was known not to have many possessions and we’ve seen about five or six references of him giving things away.”
If they fetch the highest bid of £50,000, it would be the most expensive item the auction house has ever sold.
The current record was set in 2018 after it sold comedian Robbie Barker’s script for the sketch Four Candles for £31,000.
Mr Stowe described the vendor’s disbelief at how much the glasses could make, with interest from potential buyers from all over the globe, particularly in India.
The glasses will go on sale on August 21.