Brown Brothers Harriman has signed a new 410,000 square foot lease at 50 Post Office Square, a landmark redevelopment project in the heart of downtown Boston.

Brown Brothers Harriman (BBH), America’s oldest, private financial institution and partnership, will occupy the historic, fully renovated office building this fall.

Cushman & Wakefield’s Rob Griffin, Dave Martel and Gil Dailey as well as WilmerHale LLP’s Paul Jakubowski and Kevin Bernier represented Brown Brothers Harriman in this lease transaction.

The CB Richard Ellis – N.E. Partners, LP team of Andy Hoar, Ogden White, David Fitzgerald and Tim Lyne as well as Goodwin Procter LLP’s Alex Randall and Katie Murphy represented the building ownership, Bentall Kennedy and CV Properties LLC.

50 Post Office Square, formerly 185 Franklin Street, was originally constructed in 1947 as the headquarters for the New England Telephone & Telegraph Company, the regional division of the American Telegraph & Telephone Company (AT&T). The building sits in the heart of the Financial District directly fronting Post Office Square Park.

CV Properties LLC and a Bentall Kennedy advisory client purchased the building from Verizon at the end of 2008.

Bentall Kennedy as the landlord and CV Properties LLC as the developer partnered to revitalize 50 Post Office Square. The restoration will incorporate sustainable design elements, updated amenities and new retail opportunities while paying homage to the meaningful history of the iconic building.

The building is currently undergoing extensive renovations including lobby rebuild, new entries at Post Office Square and High Street, a 100-car parking garage, and infrastructure upgrades. Sidewalk retail tenants include Pret A Manger, TD Bank and TD Ameritrade.

“This landmark lease is arguably the most important commitment to Boston’s Financial District in the past decade and will serve as BBH’s Boston headquarters for years to come,” said Cushman & Wakefield’s Dave Martel.