American collector Steve Wynn bought the work, which had been largely overpainted by a Rembrandt pupil. A recent cleaning revealed it as a self-portrait, a Sotheby's spokeswoman said, speaking on condition of anonymity.
The signed painting — dated 1634 and depicting Rembrandt at age 28 — will be displayed at Wynn's public gallery in Las Vegas, the Wynn Collection, the spokeswoman said.
She added it was "100 percent certain" that the price Wynn paid was a record for a Rembrandt self-portrait sold at auction, though she could not give a figure for the previous highest price. Other Rembrandt paintings have recently sold for more than $30 million.
The work auctioned Thursday is one of about 40 surviving Rembrandt self-portraits that are paintings; about 40 others are etchings or drawings, Sotheby's said.
It was likely painted over in Rembrandt's studio less than five years after he completed the work. The altered painting depicted a Russian nobleman in a tall Russian hat, with long hair, a mustache, a goatee beard, a fur cape and gold chains.
The underlying self-portrait was hidden for 365 years, until the Rembrandt Research Project — a group of scholars who authenticate the hundreds of paintings by the 17th-century master — began investigating the piece in 1995 at the request of its owner. Sotheby's said only that the owner was a descendant of Paul Page, a French art collector and dealer.
Although the portrait resembled Rembrandt and bore his signature, researchers at first felt it could not be genuine because it lacked the master's finesse. It took them six years to remove the layers of added paint with a scalpel.
The restored portrait shows the artist with medium-length curly hair, a slightly upturned mustache and a beret, and features dramatic diagonal lighting. In it, Rembrandt van Rijn, who lived from 1606 to 1669, has the familiar round chin and gentle eyes of many other self-portraits.
The Rembrandt House Museum in Amsterdam announced in January that the wood-panel painting, measuring 44 by 34½ inches, had been identified as a self-portrait. It was put on display at the museum for several months.
The Wynn Collection in Las Vegas features 19th- and 20th-century American and European art, including works by Picasso, Manet and Matisse. Its owner, who bid for the Rembrandt painting by phone, is a developer and former owner of Mirage Resorts.
Sotheby's said the painting auctioned Thursday is one of only three painted Rembrandt self-portraits in private collections.
Another belongs to the Duke of Sutherland and is on loan to the National Gallery of Scotland in Edinburgh. The owner of the third has not been identified.