The near 300,000 sq ft project is the next in the development pipeline following contract awards to Laing O’Rourke and Skanska earlier this year for the Soho Place Crossrail overstation and an Old Street office project.
The developer is also looking to start a smaller retail-led project at Holden House on Oxford Street.
Derwent said it would now progress the 10 storey project at 19-35 Baker Street, after reaching a major milestone by signing a conditional development agreement with Portman Estate.
Designed by architect Hopkins, the project will include 206,000 sq ft of offices and 51 flats with ground floor shops.
Holden House at 54-68 Oxford Street will comprise a 150,000 sq ft redevelopment behind a retained façade.
There is potential for a single flagship retail store with offices at the fast-improving eastern end of Oxford Street.