The project, which is due to be finished early next year, stands on the footprint of the former Quayside House and alongside the old Gloucester Prison site.
The new building will include two three-storey GP surgeries capable of serving more than 17,500 patients, a pharmacy, office space and ground floor parking.
Gloucestershire NHS Clinical Commissioning Group plans to replace the Gloucester City Health Centre at Rikenel and Gloucester Health Access Centre in Eastgate Street.
Phase two of the project includes a £7.5M multi-storey car park to provide 500 public parking spaces including charging points for electric vehicles.
Cllr Ray Theodoulou, Deputy Leader and Cabinet Member for Finance and Change, said: “This is a great scheme that will significantly benefit Gloucester and Gloucestershire, bringing investment and job opportunities into the city for its growing population.”