Boston’s Old City Hall will soon have a new landlord.

Local developer David Greaney has a deal in place to take over a long-term lease for the historic building on School Street, according to documents filed with the Boston Planning & Development Agency. The property is still owned by the city of Boston but the Architectural Heritage Foundation has run it under a long-term lease that Greaney acquired for $30.1 million.

Greaney and the foundation agreed to spend $5 million on repairs and upgrades over the next three years, while Architectural Heritage will use another $5.3 million from the deal to fund other historic preservation projects in Boston.

The deal is set to be approved Thursday by the ­BPDA before it can close. The building served as Boston’s seat of government for a century until the current City Hall was built in the mid-1960s. AHF took it over in 1970, rehabbed it and has operated it as offices with a restaurant on the ground floor.

Greaney’s Synergy Investments specializes in buying and upgrading older office buildings in downtown Boston and recently purchased the massive Center Plaza complex. At Old City Hall, Greaney said in a statement, he understands “the significant historical importance’’ of the property and “the obligations that come with that, and look forward to enhancing both our tenants’ and the public’s experience.’’

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.