The Grade II-listed 4 Norfolk Street site will feature 35 beds, a basement gym and spa, and a new roof-top extension for a private members’ terrace, restaurant and bar.
The approval comes as the former Old Trafford heroes prepare to open their first property, Hotel Football, next to Man Utd’s stadium on Saturday.
Giggs and Neville acquired the 1906-built Northern Stock Exchange Building for £1.5m back in 2013.
The proposed works, designed by Manchester architect AEW, will include the stripping out of most of the office accommodation to leave the existing floor structure.
Builders will also remove and replace a stair and lift core added in the 1980s.