The gemstone went to an unnamed telephone bidder. The auction was held online by Sotheby's in Hong Kong due to the pandemic.
The diamond was taken from a 271-carat stone which was discovered at a Canadian mine in 2018.
Only seven other diamonds larger than 100 carats and of the same quality have gone under the hammer.
The stone did not have a reserve price - a minimum price that the seller is willing to accept for an item.
It is the first time in history that a diamond has sold at auction this way.
Sotheby's described the diamond as "flawless" and said it was "difficult to overstate its rarity and beauty".
Tobias Kormind, managing director of online jeweller 77 Diamonds, said the buyer had "bagged a bargain".
He said that by not having a reserve price, the seller had made a "brave decision that has come back to bite them".
In 2017, a necklace featuring a 163-carat diamond fetched $33.7m at a Christie's event in Geneva. The diamond, taken from a 404-carat stone in Angola, is said to be the largest diamond ever presented at auction. The buyer's identity was not revealed.
The same year, a rare pink diamond weighing just under 19 carats fetched 50.3m Swiss francs (£42.3m) at auction, a record price per carat.
The price of around $2.6m per carat marked a world record for a pink diamond, according to the Europe head of auction house Christie's.