Cake has held the account since 2011 and declined to re-pitch.
The ongoing brief will see Mischief work on two new attractions for the theme park in 2016: the Rollercoaster Restaurant, and Galactica – Alton Towers’ first virtual reality rollercoaster.
Mischief will report to Liz West, media relations manager at Alton Towers Resort.
West said Mischief had "a track record of delivering exciting creative campaigns, great strategic understanding but it also regularly reacts to the news agenda and turns stories around at the speed of life".
The Alton Towers account will be led by Mischief associate director Jess Buttress and creative director Damon Statt.
Last year Alton Towers faced a PR nightmare when a total of 16 people were injured in what witnesses described as a mid-air "car crash" on one of its rides - the park dealt with the crisis well, although the same could not be said for a personal injury law firm that Tweeted about the accident.