The Rothschild Mansion, a six-story townhouse on Manhattan’s Upper East Side, sold for $25 million, the price sought when the home was put on the market almost seven years ago, said a person with knowledge of the deal.

The person asked not to be identified because the details are private. The Century Foundation, owner of the 11,300-square- foot (1,050-square-meter) property since 1958, will relocate to the financial district at the end of this month, said Derek Newton, a spokesman for the think tank, which analyzes U.S. public policy.

The townhouse, at 41 E. 70th St. between Park and Madison avenues, is “a diamond in the rough in the perfect location with the perfect garden,” according to the sales listing by Paula Del Nunzio, a broker at New York-based Brown Harris Stevens. She declined to comment on the sale.

The deal for the property, under contract since February, is poised to be completed this month. The mansion was built in 1929 for retailer Walter N. Rothschild, and his wife, Carola Warburg-Rothschild, according to the listing. It includes access to a garden named after Arthur Lehman, the son of a Lehman Brothers Holdings Inc. founder, who once lived next door.

The townhouse was listed for $25 million in November 2005, according to real estate website StreetEasy.com. It was withdrawn then returned to the market with an asking price of $35 million in July 2007, as Manhattan apartment values were approaching their peak. The mansion has been for sale since then, with the price decreasing three times over two years to $25.5 million. In December 2010, as values of luxury properties were climbing, the owners raised the price to $30 million, according to StreetEasy.

The median price of Manhattan luxury properties, defined as the top 10 percent of all deals by price, was $4.07 million in the third quarter, a 2.6 percent drop from a year earlier, New York appraiser Miller Samuel Inc. and brokerage Prudential Douglas Elliman Real Estate said in a report today.