"Tete de Femme (Jacqueline)", a portrait of the Spanish artist's second wife, had not been seen in public since 1967 and was expected to fetch up to four million pounds at the sale Tuesday in London, said Christie's auctioneers.
The 1963 painting had never been offered at auction and remained in the same collection since 1981.
"Tete de Femme (Jacqueline)" fetched 8,105,250 pounds, said Christie's, and was just one of a string of masterpieces up for sale which also included works by Renoir and Matisse.
Picasso's wife Jacqueline was said to have had a short neck and the painter would often exaggerate its size in portraits.
Christie's would not reveal the identity of the buyer.
The Impressionist and Modern Art Evening Sale raised a total of 76.9 million pounds, with four works selling for more than five million pounds, said Christie's.
The sale sent a signal that "demand is high and that knowledgeable buyers from around the world are committed to acquiring works of art," said Giovanna Bertazzoni, Christie's director of Impressionist and Modern Art.
Keep up with the latest business news from the region with the Emirates Business 24|7 daily newsletter. To subscribe to the newsletter, please click here.