The move was announced by John P McGarry, the agency's chief executive, who said: "For quite some time, McGarry Bowen's clients have been asking us to expand our footprint to support them in other markets.
"In the same way we've added depth in our service offerings to respond to our clients' needs – adding digital, design, direct, and media services – we want to provide our partners with the geographic breadth they need."
Founded and headquartered in New York, McGarry Bowen opened a second office in Chicago in 2007. The head of the Chicago office, Tim Scott, will primarily head the London office and lead a major FMCG brief. The McGarry Bowen office will be first based in Dentsu's London offices.
The office will launch with around 10 staff, with recruitment underway.
McGarry Bowen's plan for entering the European market will be focused on its existing roster of clients, which includes InBev, Disney and Reebok.
The Chicago office now has 70 staff, and McGarry said that he would be looking to "mirror that success in London".
It is also understood that there will be further territory expansion with a Mexico office adding spice to the mix.
McGarry said: "We will certainly revise our operations to reflect local tastes and preferences, but we won't move away from what has made us who we are as an agency.
"We will certainly revise our operations to reflect local tastes and preferences, but we won't move away from what has made us who we are as an agency."
Tim Andree, Dentsu's executive officer for the Americas and Europe, said: "McGarry Bowen is legendary in the industry for their client relationships and for making creative work that works.
"Expanding into other markets where their clients operate is a natural outgrowth not only of McGarry Bowen's current client strategy, but of Dentsu's vision for how an agency network can nurture and support an agency and its clients."
In September last year, telecoms firm Verizon Wireless appointed McGarryBowen to handle a marketing project for its highly-anticipated Verizon Android phone.