Holding company MSQ is consolidating its operations into a redeveloped office in Covent Garden on the back of an acquisition and organic growth.
The group acquired rival Be Heard last year, merging Be Heard's digital media shop agenda21 into its own Walk-In Media offering.
With its headcount up from 550 to 850 people in 18 months MSQ decided to take out a 10-year lease on the 20,315 square feet offices across two floors at 34 Bow Street, opposite The Royal Opera House.
It will move all its agencies' London headquarters into the building later this year.
Its previous offices were on Tottenham Court Road, while Be Heard was based in premises in Soho.
MSQ plans to move the London bases for all nine of its agencies into the new location; with the exception of Holmes & Marchant (Shanghai), Smarts (Belfast), Stein IAS (Manchester) and twentysix (Leeds), which will have their headquarters based elsewhere.
According to the agency, the property deal is one of largest recorded in the UK capital so far in 2021.
MSQ said the move would enable it to create a working environment suited to a post-COVID world. Using a hybrid working model. the office will provide staff with a flexible working space. It will also be carbon negative, using materials from environmentally friendly sources where possible.
34 Bow Street is still in redevelopment. Once the process is completed, MSQ will undergo a phased move into the building.
Peter Reid, MSQ's chief executive, said: "This is another key milestone in the evolution of MSQ. We've grown rapidly over the past 18 months and I'm excited to move into a vibrant new working space that reflects our new size and ambition.
"The pandemic has changed the circumstances in which we'll work forever, and we'll work hard to understand and adapt to the different ways that our team want to work going forward, all with the ultimate end goal of helping our clients build more emotionally intelligent and connected brands."
MSQ bought Be Heard Partnership for £6.2m in September last year. It comprised research business Freemavens, web and digital agency MMT Digital and digital media shop agenda21. The group has also opened offices across the Atlantic in the past year – Smarts in New York and The Gate in San Francisco.
Earlier this week, We Are Social announced that it was slashing its office space by half in preparation for its staff returning later this year.