The consultant will be the anchor tenant at the former home of ad agency Saatchi and Saatchi.
Demolition is currently underway at the site where Multiplex will build a 380,000 sq ft mixed-use scheme which is due for completion by the end of 2019.
Derwent has also agreed to sell its building at Fitzroy Street for £197m to Arup who occupy the entire property on a long-term rental agreement.
John Burns, Chief Executive Officer of Derwent London, said: “We are delighted to continue our long standing and close relationship with Arup in this mutually beneficial transaction.
“We have been able to facilitate the upgrade of Arup’s London headquarters and Arup will be the first occupier anchoring our major 80 Charlotte Street development.
“This complex transaction further de-risks Derwent London’s development programme, and is evidence of our asset management and letting skills, the desirability of our product and the advantage of owning a cluster of property in an attractive location.”
David Whittleton, Deputy Chair and Group COO of Arup Group, said: “This innovative deal offers real benefits to both Derwent and Arup, and was possible because of the strong and trusting relationship developed between our firms over many years.
“Arup is very pleased to have been able to secure its London future in quality space in the rapidly improving Fitzrovia area, where the firm has been based since inception, at attractive and predictable costs. We look forward to many more collaborations in the years ahead.”