According to Sotheby's, the selling price of the rectangular-shaped blue stone is the highest price paid per carat for any gemstone at auction.
The celestial stone, mounted on a platinum ring, was found in Cullinan mine in South Africa last year, and was the centrepiece of Sotheby's semi-annual sale in Geneva, reports The Telegraph.
The anonymous phone bidder, who won after a 15-minute war, has yet to name the gem.
"I was a little bit concerned in this market," said David Bennett, head of jewellery for Sotheby's Europe and Middle East.
The previous record price for a fancy vivid blue diamond was 5.2 million pounds, including commission, for a stone weighing 6.04 carats at sale in Hong Kong in Oct 2007, also by Sotheby's.