The listed Ewart Building on Bedford Street has been empty for more than 25 years.
However, Belfast City Council's planning committee granted approval on Tuesday for its conservation, refurbishment and extension.
The development will also include a 17-storey tower behind the Ewart Building, with 18,000 sq metres of office space.
A new landscaped public space will also be on the site.
The development is the second phase of the Bedford Square development scheme.
The first phase of the project was completed in 2006, with the headquarters of Invest Northern Ireland.
Developers McAleer & Rushe said the planning approval represented "a welcome boost to the Belfast office market".
Director Stephen Surphlis said: "This will bring a landmark building back into active use after many years of vacancy and help to alleviate the shortage of grade A [office] space in the city."
Ulster Unionist councillor Peter Johnston, the chair of the Belfast City Council's planning committee, said a balance would be struck "between meeting the needs of a forward-thinking, modern city and preserving the more important aspects of its heritage".
He added: "It's great to see this important, historic building being brought back into use in a way that will see it play its part in the continued prosperity of the city, just as it did when it was first built in 1870."
A former linen warehouse in Belfast city centre is to be developed into office suites.