Work will start this month on the revamp of the historic Assay Office in Birmingham's Jewellery Quarter after it was given the green light by city planners.
TCN UK, which acquired the building last year, plans to create to new business space in the Newhall Street building aimed at small companies and build 32 apartments on the rear car park.
Richard Pearce, from TCN UK, said: "We are delighted to have received planning consent from the planning committee, allowing us to bring our vision to life.
"Works will start immediately on the first phase, the transformation of the existing building into office accommodation."
The project was designed by Birmingham practice Glenn Howells Architects and comprises 30,000 sq ft of new office space across 27 separate units which is due to be available to tenants from next spring.
The residential block comprises 18 one-bedroom and 14 two-bedroom apartments, 13 parking spaces and 32 for bikes.
The façade and many of the internal historical features of the Grade II listed building have been incorporated into the plans and there will be a communal space in the basement, designed to facilitate collaborative working among occupiers.
Michael Cruise, studio director with Glenn Howells Architects, said: "Integral to our design is the strong character of the existing building while the new build residential scheme will complete the missing corner of St Paul's Square.
"This includes the use of traditional brickwork which responds to the sensitive context and interesting articulation of the area and pays reference to the industrial heritage of the Jewellery Quarter."
The Assay Office moved to a new, purpose-built home earlier this year in Icknield Street, having been in the Newhall Street since it was built in 1878.
Pictures: Inside Birmingham's Assay Office