Ewan McGregor
Rodney Copperbottom (voice)

Robin Williams
Fender (voice)

Halle Berry
Cappy (voice)

Amanda Bynes
Piper (voice)

Mel Brooks
Bigweld (voice)

Jim Broadbent
Madame Gasket (voice)

Greg Kinnear
Ratchet (voice)

Stanley Tucci
Herb Copperbottom (voice)

Dianne Wiest
Mrs. Copperbottom (voice)

Drew Carey
Crank (voice)

Harland Williams
Lug (voice)

Jennifer Coolidge
Aunt Fanny (voice)

Paul Giamatti
Tim the Gate Guard (voice)

Natasha Lyonne
Loretta Geargrinder (voice)

Chris Wedge
Wonderbot / Phone Booth (voice)

Dan Hedaya
Mr. Gunk (voice)

Marshall Efron
Lamppost / Toilet Bot / Bass Drum / Microphone

Terry Bradshaw
Broken Arm Bot (voice)

Al Roker
Mailbox (voice)

Lucille Bliss
Pigeon Lady (voice)

Jay Leno
Fire Hydrant (voice)

Lowell Ganz
Mr. Gasket (voice)

Paula Abdul
Watch (voice)

Jackie Hoffman
Water Cooler (voice)

Brian Scott McFadden
Trashcan Bot (voice)

Tim Nordquist
Tin Man (voice)

James Earl Jones
Voice Box at Hardware Store (voice)

Damien Fahey
Stage Announcer (voice)

Stephen Tobolowsky
Bigmouth Executive / Forge (voice)

Jansen Panettiere
Younger Rodney (voice)

Will Denton
Young Rodney (voice)

Crawford Wilson
Young Rodney (voice)

Dylan Denton
Youngest Rodney (voice)

Jennifer Perito
Additional Voices

Alan Rosenberg
Jack Hammer (voice)

Lara Cody
Additional Voices

Cooper Cowgill
Additional Voices

David Crommett
Additional Voices

Darin De Paul
Additional Voices

Dann Fink
Additional Voices

Timothy Gulan
Additional Voices

Ray Iannicelli
Additional Voices

Sondra James
Additional Voices

Vanessa Lemonides
Additional Voices

Marcus Maurice
Additional Voices

David Rossmer
Additional Voices

Bruce Winant
Additional Voices / ADR Loop Group

Chris Moyles
Stage Announcer (voice)

Chingy
DJ Robot (uncredited)

Sean Garnhart
Diesel (uncredited)

Paul Urmson
Diesel (uncredited)

Randy Jackson
Watch #2 (voice) (uncredited)

James Brown
Diesel (archive footage) (uncredited)