St Andrew Street was set to close from 5am this morning, while Shandwick Place is due to close on January 14, with a series of diversions being put in place for traffic at both locations.
The move will allow all remaining utility work to get under way ahead of the start of major infrastructure work in February.
The east side of St Andrew Square – including North and South St Andrew Street will be closed to vehicles, with all traffic switched to the west side. The work site will extend down on to Princes Street and to the right as far as Waverley Bridge.
The council stressed that there will still be access to shops and premises, while additional support will be put in place for business deliveries.