It will adopt Henley’s small-events arm and advertising division, as well as its corporate clients, which include Siemens.
The purchase sees RJH’s staff count grow from 14 to 26 people and it will retain the Henley International name.
CEO Jack Cassidy said: ‘This gives us a corporate balance and opportunities to provide global services.’
Henley director James Tate has been promoted to the RJH board.
RJH has also announced plans to open offices in New York and Washington DC and is recruiting three staff to join its London office.