The brief covers all elements of the Chessington Resort in Surrey, including the theme park, Chessington Zoo, Sea Life Centre and Holiday Inn Chessington.
Chessington formerly used Blue Zebra, which was invited to repitch.
The Clarion team will be overseen by MD Amanda Meyrick.
Mayrick commented: ‘We will be working with Chessington to deliver a PR campaign which further establishes the Chessington Resort as Britain’s wildest adventure.’
Other activity during 2011 will include the second annual search for Britain’s Most Adventurous Family, as well as the 80th anniversary of Chessington Zoo.
Chessington World of Adventures Resort is part of The Merlin Entertainments Group, which also includes Madame Tussauds, Legoland and Alton Towers Resort.