GE Healthcare has signed a 15-year lease for 209,855 square feet of space at 200 Forest St. in Marlborough, the former Hewlett-Packard site being redeveloped by Atlantic Management of Framingham.

Atlantic Management acquired the 110-acre office park for $8.7 million in 2012 and gained local approval to convert the 1960s-era relic into a mixed-use development including a hotel, apartment complex and 50,000 square feet of retail shops.

The New Jersey-based GE division announced last August it would relocate its headquarters to 200 Forest St. by consolidating its operations from Princeton and Piscataway, N.J. The new U.S. headquarters will house more than 500 employees in its research, bioprocessing, medical imaging, in vitro diagnostics and services segments.

GE Healthcare’s lease begins April 21. The company is building out the office and lab space and is expected to occupy the building at 200 Forest St. this summer, said Joseph Zink, CEO of Atlantic Management. The building has 120,000 square feet of space available.

Quest Diagnostics signed on as the first office and lab tenant and occupied its 204,000-square-foot space at 200 Forest St. in June.

"The momentum has been very positive and those are two great credit tenants," Zink said. "People want to be in a campus environment to help them attract and retain employees."

The first move-ins will begin in March at the 350-unit Avalon Marlborough apartment complex, Zink said. AvalonBay Communities is advertising one-bedroom apartments starting at $1,480 and two-bedroom units from $1,780.

Construction of a 165-room Hilton Garden Inn geared to business travelers started in December and is scheduled for completion in spring 2016.

Atlantic Management is in negotiations with tenants for 50,000 square feet of new restaurant and retail space.

An adjacent 25-acre site at 2 Results Way has 170,000 square feet of existing space available. Alternatively, the building could be demolished for a build-to-suit project up to 350,000 square feet.