GFP Real Estate and the Northwind Group have signed a contract to buy 7 Hanover St. for $310 million, equating to roughly $350 per square foot, but renovations will increase the all-in future costs.

The 904,500-square-foot office building is perched between Pearl and Water streets adjacent to Hanover Square in the Financial District of downtown Manhattan. The building also has view corridors to the East River over the low-rise portion of 55 Water St.

The building is being purchased from its developer/owners, the Milstein family and Swig Weiler and Arnow Management. They had granted tenant Guardian Life Insurance a $147 million purchase option back in 1998, when downtown wasn’t in such hot shape. The option was exercised last spring by Guardian, which leases most of the 27-story tower and had renewal options through 2044, city documents show.

The 158-year-old insurance company will leave it vacant when the sale closes in October 2019 and will move to 10 Hudson Yards in a 148,000-square-foot sublease from Coach.

Douglas Harmon and Adam Spies led the Cushman & Wakefield team of Adam Doneger, Josh King and Marcella Fasulo in marketing the building for Guardian. In 2017, the team sold a 49 percent stake in One Liberty on behalf of Brookfield to Blackstone, which revalued it at $1.52 billion, and 80 Broad to Invesco for $235 million from Broad Street Development.

Formerly known as Newmark Holdings, GFP is led by chairman Jeffrey Gural, co-CEOs Eric Gural and Brian Steinwurtzel, principal Jane Gural-Senders and AnnyRose Pahl, general counsel. The name change — announced in October 2017 — prevented confusion when Jeffrey Gural stepped down as chairman of the now-public Newmark Knight Frank.

GFP already has a relationship with Northwind, led by Ran Eliasaf, as they are already redeveloping 40 Exchange Place.

The red-brick edifice at 7 Hanover was designed by Emory Roth & Sons in 1983 and renovated in 2005. It resembles a residential building but, with downtown’s Class A office vacancy rate of 9.5 percent, it is likely the buyers will bring updated technology and keep it as offices.

The companies did not reply to requests for comment.