The decision of Portsmouth City Council planning officers paves the way for work to preserve its condition, including rebuilding the brickwork buttress cap and window repairs.
A decision notice approving the application said the work would help 'protect the special historic and architectural interest of the listed building'.
The council, which owns the building, applied in April for permission for the repairs, saying they were needed to maintain the integrity of the structure while allowing ventilation systems to be upgraded.
The plans will allow the reconstruction of the building's parapets, repointing and a series of wall repairs to take place.
Drainage improvements, re-roofing and the installation of mechanical ventilation systems for the toilets and the Matcham Bar are also included in the proposals, aimed at reducing future damage to the structure of the building.
The work has to begin within three years.