Der skrupellose Gangster Mickey Cohen (Sean Pean) hat Los Angeles in seinem Würgegriff. Im Kampf gegen das Verbrechen und die wild wuchernde Korruption ist Chief Bill Parker (Nick Nolte) gezwungen, zu extremen Mitteln zu greifen. Er kann Kriegsheld Sgt. John O'Mara (Josh Brolin) dafür gewinnen, eine Spezialeinheit zusammenzustellen, um knallhart Selbstjustiz zu üben. Ihr Ziel sind keine Verhaftungen… sondern Krieg. Während die Stadt zu explodieren droht, wird Sgt. Jerry Wooters (Ryan Gosling) widerwillig in den Konflikt gezogen, als er Grace Faraday (Emma Stone) verfällt, einer eleganten Schönheit, die Cohen als sein Eigentum beansprucht … Basierend auf wahren Begebenheiten, erzählt Gangster Squad die lange unter Verschluss gehaltene Geschichte der Polizei-Einheit, die für L.A.s Seele kämpfte.
| Sean Penn | Mickey Cohen |
| Holt McCallany | Karl Lockwood |
| Wade Williams | Rourke |
| James Landry Hébert | Mitch Racine (as James Hébert) |
| Ambyr Childers | Milk Skinned Blonde |
| Josh Brolin | Sgt. John O'Mara |
| Mick Betancourt | Detective Sgt. Will Hendricks |
| Mac Brandt | Bruiser |
| Brandon Molale | Jimmy 'Bockscar' Knox |
| Michael Papajohn | Mike 'The Flea' |
| Jeff Wolfe | Giovanni Vacarezza |
| Anthony Molinari | Lorenzo Molinari |
| Austin Highsmith | Patty |
| Austin Highsmith Garces | Patty |
| Ryan Gosling | Sgt. Jerry Wooters |
| Neil Koppel | Max Solomon |
| Jack McGee | Lt. Quincannon |
| Steve Jablonsky | Composer |
| Mireille Enos | Connie O'Mara |
| Dion Beebe | Cinematographer |
| Evan Jones | Neddy Herbert |
| Alan Baumgarten | Editor |
| James Carpinello | Johnny Stomp |
| James Herbert | Editor |
| Troy Garity | Wrevock |
| Maher Ahmad | Production Designer |
| Austin Abrams | Pete |
| Lucy Davenport | Slapsy Maxie's Singer |
| Sullivan Stapleton | Jack Whalen |
| John Aylward | Judge Carter |
| Dennis Cockrum | Elmer Jackson |
| Jack Conley | Sheriff Biscailuz |
| Emma Stone | Grace Faraday |
| Riel Paley | City Hall Reporter |
| Michael C. Mahon | City Hall Reporter |
| David Fleischer | City Hall Reporter |
| Nick Nolte | Chief Parker |
| Josh Pence | Officer Darryl Gates |
| Anthony Mackie | Officer Coleman Harris |
| Sky Paley | City Hall Reporter |
| De'aundre Bonds | Duke Del-Red |
| Robert Patrick | Officer Max Kennard |
| Michael Peña | Officer Navidad Ramirez |
| Giovanni Ribisi | Officer Conwell Keeler |
| Maxwell Perry Cotton | Keeler's Son |
| Haley Strode | Keeler's Wife |
| Scott Beehner | Club Figaro Reporter |
| Matt Knudsen | Club Figaro Reporter |
| Lucas Fleischer | Club Figaro Reporter |
| Jon Polito | Dragna |
| Lance Barber | Comanche |
| Michael Bacall | Comanche |
| Dale Gibson | Burbank Cop |
| Rick Marcus | Burbank Cop |
| Mickey Giacomazzi | Hatchetman |
| Cazimir Milostan | Desk Officer |
| Darrell Davis | Officer Wyler |
| Don Harvey | Officer Funston |
| Anthony De Longis | Burbank Jail Thug |
| Michael Owen | Burbank Jail Thug |
| Tom Hallick | El Dorado Investor |
| Esther Scott | Letty |
| Jonny Coyne | Grimes |
| Christopher Doyle | Edgar Beaumont |
| Max Daniels | Jeffrey Clark |
| Danny Wynands | Grenade Goon |
| Derek Mears | Bridge Goon |
| Yvette Tucker | Carmen Miranda |
| Derek Graf | El Dorado Guard |
| Anne Leighton | Crying Woman |
| Ken Edling | Detective |
| Hilary Fleming | Dancer |
| Debby Gerber | Plaza Runner |
| Tina Mayer | Dancer |
| Marcy McCusker | Dancer |
| Chris Moss | Dancer |
| Kevin James Sporman | Dancer |
| Forrest Walsh | Dancer |
| Kevin Young | Burn Victim |
| Christopher Aber | Reporter (uncredited) |
| Pamela Adamic | Drugged-Out Girl (uncredited) |
| Michael Arturo | Dealer (uncredited) |
| Kojo Asiedu | Bar Patron (uncredited) |
| Robert T. Barrett | LAPD Cop (uncredited) |
| Bob Bouchard | Movie Patron (uncredited) |
| Mark Hunstable | Art Director |
| Greg Cannone | Slapsy Maxie's Waiter (uncredited) |
| Timothy David O'Brien | Art Director |
| Pamela Cedar | Gambler (uncredited) |
| Dean Wolcott | Art Director |
| Michael Copeland | Water pitcher waiter (uncredited) |
| Gene Serdena | Set Decorator |
| Clint Corley | Man at Union Station (uncredited) |
| Mary Zophres | Custome Designer |
| Tiffany Daniels | Club Alabam Dancer (uncredited) |
| Diana Acrey | hair stylist |
| Eddie Davenport | Goon Gunman (uncredited) |
| Argo | hair stylist |
| Seth Di Marco | Goon (uncredited) |
| Myriam Arougheti | Makeup Artist |
