'A lot of our clients are based in London so our account executives are always flying there,' agency partner Simon Halls told PRWeek US.
The Interpublic Group-owned outfit has offices in Hollywood and New York.
Its website lists AOL, Motorola, Levi's and Louis Vuitton as brand clients.
PMK/HBH, run by LA-based Pat Kingsley, has yet to reveal who will head its London office.
One London film and celebrity PRO told PRWeek: 'I suspect they're wanting to boost their European representation for their brand clients but that's a very competitive market here. If they're wanting to make a success of representing more British celebrities it will depend entirely on who they hire to work for them.'