It’s official: Winthrop Square Garage will be turned into one of Boston’s tallest towers

An artist’s rendering of the proposed development at the site of the Winthrop Square Garage.Handel Architects

City officials have reached a deal with Millennium Partners to turn the shuttered Winthrop Square Garage into one of Boston’s tallest towers.

Under terms disclosed Tuesday, Millennium will pay $10 million upfront for the site, $92 million more when it obtains a building permit from the city, and another approximately $50.8 million as it closes on condominiums in the 750-foot condo and office tower it plans to build on the site of the closed garage. The nearly $153 million total is slightly more than what the company originally offered during the bidding process.

The deal gives Millennium until the end of 2017 to complete permitting on the project, with additional payments if it drags beyond then. But Millennium executive Joe Larkin said the company expects to break ground by September or October.

“We’re eager to get going,” Larkin said.

The city’s Public Facilities Commission Tuesday began the two-step process of turning the city-owned garage over to Millennium, by voting to transfer ownership to the Boston Planning and Development Agency. Next the BPDA must finalize its deal with Millennium.

The two sides have been negotiating over the last two-plus months, since the BPDA chose Millennium’s plan for the hotly-contested site.

At $102 million, Millennium’s lump sum will be $2 million more than its initial offer, which was by far the highest of six bids for the site. And the firm agreed to pay $10 million upfront, which the city will keep even if the project stalls. It can use $2.5 million of that money to demolish the garage, if demolition starts by June 15.

“Even if the developer fails to complete the purchase the city will either end up with $10 million, or $7.5 million and the garage demolished,” said assessor Ron Rakow.

Meanwhile, city officials agreed to seek changes to a state law governing how much shadows new buildings can cast on Boston Common, suggesting Millennium’s 750-foot tower, situated one-third of a mile from the Common, could cast a long shadow indeed. BPDA staff said all six of the proposals would have cast at least a sliver of a new shadow on the Common, and the changes are mainly technical.