Kevin Hart as George Beard (voice)

Thomas Middleditch as Harold Hutchins (voice)

Ed Helms as Mr. Krupp / Captain Underpants (voice)

Nick Kroll as Professor Poopypants (voice)

Jordan Peele as Melvin (voice)

Kristen Schaal as Edith (voice)

DeeDee Rescher as Ms. Ribble (voice)

Brian Posehn as Mr. Rected (voice)

David Soren as Tommy (voice)

Mel Rodriguez as Mr. Fyde (voice)

Susan Fitzker as Ms. Dayken (voice)

Lynnanne Zager as George's Mom (voice)

Tiffany Lauren Bennicke as Sad Girl (voice)

James Ryan as Mime (voice)

Leslie David Baker as Officer McPiggly (voice)

Sugar Lyn Beard as Goodie Two-Shoes Girl (voice)

Lesley Nicol as Nobel Moderator (voice)

Chris Miller as Nobel Audience Member (voice)

Coco Soren as Balloon Girl (voice)