Boris Johnson has given the go-head to the redevelopment of 80 Charlotte Street & 65 Whitfield Street in Camden despite the project previously being blocked by Camden Council.
The block is currently home to ad firm Saatchi & Saatchi.
In June the Mayor exercised his power to take over the application after the council refused developers Derwent London permission for the scheme.
City Hall defended the decision to sideline the local council on the grounds that the development will raise £1.6m for the Crossrail scheme and create new jobs.
The Mayor said he had given the go-ahead subject to developers agreeing to ensure 16 of the planned 55 homes are affordable, contribute £1.6m to Crossrail and make further contributions to local facilities and street improvements.
Mr Johnson commented: “The capital’s adland, centred around Charlotte Street, has developed an international reputation for creativity and I have no doubt that its redevelopment can only be good news for both the West End and the wider London economy.
“I can find no reason to refuse permission and am of the firm view that this ambitious and important redevelopment should go ahead.”