Carrey, who starred in the film version of How the Grinch Stole Christmas, will voice Horton, the elephant who says a person’s a person no matter how small.
The 20th Century Fox project will be the first time for Carrey to work on a completely animated film. Carrell plays the Mayor of the town, a distinguished figure who is too small for Horton to see.
Horton Hears a Who is the story of an elephant who tries to save the village of tiny people who are no larger than a grain of sand.
The film was inspired by the 1954 book, written by Ted Geisel, under the pen name of Dr. Seuss. The books of Dr. Seuss have sold more than 200 million copies and have been adapted into 15 different languages.