The broker responsible for the eye-popping $1.8 billion sale of 111 Eighth Ave. to Google has won the high-stakes competition to market the 36-story Sony building at 550 Madison Ave.

Eastdil Secured, which is now selling Worldwide Plaza, another mega-building on the West Side, sealed the deal, The Post has learned.

The possibility of a sale of the 800,000-square-foot tower was first reported by The Post in June.

In mid-September, in a memo to employees, Nicole Seligman, president of Sony Corp. of America, said it would be hiring a real estate consultant for a possible sale and possible future move.

The city’s major brokerages, including CBRE, Cushman & Wakefield, Jones Lang LaSalle, Newmark Grubb Knight Frank and Eastdil were interviewed or submitted proposals to represent Sony for the coveted assignments to sell the building and search for new space, sources said.

Doug Harmon and his Eastdil investment sales team have dominated the city’s office sales market over the past decade, according to Real Estate Alert. They were responsible for the $1.8 billion sale of 111 Eighth Ave. to Google and are in the middle of selling Worldwide Plaza, another mega-building, which is expected to garner well over $1 billion.

Eastdil is strictly an investment sales brokerage so another company will be hired to lead the search for a new city headquarters.

Possibilities include a move to a new building in Hudson Yards or the World Trade Center, or even the Time Warner Center, which will soon be on the block.

Eastdil and Sony did not return e-mails and calls for comment.