Viacom International Media Networks - one arm of the wider Viacom business - will use the agency for corporate work highlighting its multi-platform activity.
Included in the new international brief is awareness-raising for events such as the MTV Europe Music Awards and promoting opportunities for commercial partnerships with the channels.
News of the appointment comes amid record ratings for the European awards, though US based MTV Video Music Awards - which the agency will not work on - saw viewer numbers halve last year.
W Communications head of media Becky Charles will lead the work and report to the VIMN Corporate Communications team.
Agency founder Warren Johnson said: 'It's an exciting time for Viacom as TV and digital collide to create a world of connected media and immersive experiences. Our role is to hero the amazing work its brands like MTV are doing.'