| Billy Crystal | Mike Wazowski (voice) |
| John Goodman | James 'Sulley' Sullivan (voice) |
| Helen Mirren | Dean Hardscrabble (voice) |
| Steve Buscemi | Randall Boggs (voice) |
| Peter Sohn | Scott 'Squishy' Squibbles (voice) |
| Joel Murray | Don Carlton (voice) |
| Aubrey Plaza | Claire Wheeler (voice) |
| Sean Hayes | Terri Perry (voice) |
| Dave Foley | Terry Perry (voice) |
| Charlie Day | Art (voice) |
| Alfred Molina | Professor Knight (voice) |
| Tyler Labine | Brock Pearson (voice) |
| Nathan Fillion | Johnny Worthington (voice) |
| Bobby Moynihan | Chet Alexander (voice) |
| Noah Johnston | Young Mike (voice) |
| Julia Sweeney | Ms. Squibbles (voice) |
| Bonnie Hunt | Karen Graves (voice) |
| John Krasinski | Frank McCay (voice) |
| Bill Hader | Referee (voice) |
| Beth Behrs | Carrie Williams (voice) |
| Bob Peterson | Roz (voice) |
| John Ratzenberger | Yeti (voice) |
| Lori Alan | Additional Voices (voice) |
| Carlos Alazraqui | Additional Voices (voice) |
| Jack Angel | Additional Voices (voice) |
| Bob Bergen | Additional Voices (voice) |
| Gregg Berger | Additional Voices (voice) |
| Rodger Bumpass | Additional Voices (voice) |
| Neil Campbell | Additional Voices (voice) |
| Frank Oz | Fungus (voice) |
| Ava Acres | Additional Children's Voices (voice) |
| Sherry Lynn | Additional Voices (voice) |
| Paul Lazenby | Monster (voice, uncredited) |
| Aramé Scott | Additional Children's Voices (voice) |
| Joseph John Schirle | Additional Children's Voices (voice) |
| Kristen Li | Additional Children's Voices (voice) |
| Davin Ransom | Additional Children's Voices (voice) |
| Raymond Ochoa | Additional Children's Voices (voice) |
| Calum John | Additional Children's Voices (voice) |
| Montse Hernandez | Additional Children's Voices (voice) |
| Mason Cook | Additional Children's Voices (voice) |
| Makenna Cowgill | Additional Children's Voices (voice) |
| Tyree Brown | Additional Children's Voices (voice) |
| Jack Bright | Additional Children's Voices (voice) |
| Isabella Acres | Additional Children's Voices (voice) |
| April Winchell | Additional Voices (voice) |
| Colette Whitaker | Additional Voices (voice) |
| Jim Ward | Additional Voices (voice) |
| Marcia Wallace | Additional Voices (voice) |
| David Theune | Additional Voices (voice) |
| Tara Strong | Additional Voices (voice) |
| Mindy Sterling | Additional Voices (voice) |
| Joel Spence | Additional Voices (voice) |
| Betsy Sodaro | Additional Voices (voice) |
| Patrick Seitz | Additional Voices (voice) |
| Dan Scanlon | Additional Voices (voice) |
| Jan Rabson | Additional Voices (voice) |
| Cristina Pucelli | Additional Voices (voice) |
| Jeff Pidgeon | Additional Voices (voice) |
| Dannah Feinglass Phirman | Additional Voices (voice) |
| Donovan Patton | Additional Voices (voice) |
| Bret 'Brook' Parker | Additional Voices (voice) |
| Colleen O'Shaughnessey | Additional Voices (voice) |
| Laraine Newman | Additional Voices (voice) |
| David Neher | Additional Voices (voice) |
| Pam Murphy | Additional Voices (voice) |
| Matthew Mercer | Additional Voices (voice) |
| Alec Medlock | Additional Voices (voice) |
| Allan McLeod | Additional Voices (voice) |
| Mickie McGowan | Additional Voices (voice) |
| Tricia McAlpin | Additional Voices (voice) |
| Mona Marshall | Additional Voices (voice) |
| Jason Marsden | Additional Voices (voice) |
| Danny Mann | Additional Voices (voice) |
| Dawnn Lewis | Additional Voices (voice) |
| Elissa Knight | Additional Voices (voice) |
| John Kassir | Additional Voices (voice) |
| Brandon Johnson | Additional Voices (voice) |
| Jess Harnell | Additional Voices (voice) |
| Mike Hanford | Additional Voices (voice) |
| Daniel Gerson | Additional Voices (voice) |
| Teresa Ganzel | Additional Voices (voice) |
| Donald Fullilove | Additional Voices (voice) |
| Andy Fischer-Price | Additional Voices (voice) |
| Keith Ferguson | Additional Voices (voice) |
| Bill Farmer | Additional Voices (voice) |
| Paul Eiding | Additional Voices (voice) |
| Greg Dykstra | Additional Voices (voice) |
| John Cygan | Additional Voices (voice) |
| Sean Conroy | Additional Voices (voice) |
| Patrick Carlyle | Additional Voices (voice) |
| Natalie Jane Dang | Additional Children's Voices (voice) |
| Gage Davenport | Additional Children's Voices (voice) |
| Ethan Louis Samuels DiSalvio | Additional Children's Voices (voice) |
| Faith Goblirsch | Additional Children's Voices (voice) |
| Brooke Klinger | Additional Children's Voices (voice) |
| Nikolas Michailidis | Additional Children's Voices (voice) |
| Marley Pearson | Additional Children's Voices (voice) |
| Davin Doak | Additional Children's Voices (voice) |