Chenoweth, 47, will be voicing a brand-new, as-yet-unnamed character in the animated feature, produced by Lionsgate along with the toy company Hasbro, reported Entertainment Weekly.
"Meghan McCarthy and the 'My Little Pony' cast are a very talented and cohesive team, whom we're happy to be working with and we're excited about the addition of the very talented Kristin Chenoweth, as we explore new aspects of these characters and new story opportunities for the franchise," Lionsgate co-president Erik Feig said in a statement.
McCarthy, who executive produced "My Little Pony: Friendship is Magic", is writing the screenplay, while Jayson Theissen will direct the feature.