The firm revealed this morning that it will start the 367,000 st ft mixed-use development at 80 Charlotte Street in Fitzrovia during the second half of the year.
Bam Construct, Brookfield Multiplex and Mace are all understood to be in the race for the £125m building contract.
Derwent put the project on hold in July 2013, after advertising giant Saatchi & Saatchi, which has occupied the building since 1975, delayed its move away from the property.
But it has now set a date to start work on the office, residential and retail project, which has been designed by architects Make.
The project will be part refurbishment and part new build with a substantial proportion of the existing structures retained thereby cutting waste and carbon emissions whilst reducing the construction period.
The 367,000 sq ft redevelopment will include 336,000 sq ft of office, residential and retail space at 80 Charlotte Street and 31,000 sq ft of residential at nearby 65 Whitfield Street and 1-8 Whitfield Place.