| Steve Buscemi | Enoch 'Nucky' Thompson |
| Michael Pitt | James 'Jimmy' Darmody |
| Kelly Macdonald | Margaret Schroeder |
| Michael Shannon | Nelson Van Alden |
| Shea Whigham | Elias 'Eli' Thompson |
| Aleksa Palladino | Angela Darmody |
| Michael Stuhlbarg | Arnold Rothstein
(credit only) |
| Stephen Graham | Al Capone |
| Vincent Piazza | Lucky Luciano
(credit only) |
| Paz de la Huerta | Lucy Danziger |
| Michael Kenneth Williams | Chalky White |
| Anthony Laciura | Eddie Kessler |
| Paul Sparks | Mickey Doyle
(credit only) |
| Jack Huston | Richard Harrow |
| Gretchen Mol | Gillian Darmody |
| Dabney Coleman | Commodore Louis Kaestner |
| Dominic Chianese | Leander Cephas Whitlock |
| Greg Antonacci | Johnny Torrio |
| Enid Graham | Rose Van Alden |
| Robert Clohessy | Alderman Jim Neary |
| William Hill | Ward Boss O'Neil |
| Kevin O'Rourke | Edward Bader |
| Victor Verhaeghe | Ward Boss Fleming |
| Glenn Fleshler | George Remus |
| Bill Sage | Solomon Bishop |
| Joseph Aniska | Agent Sawicki |
| Matty Blake | State Trooper |
| John Bolton | Carl Switzer |
| Joel Brady | Agent Clarkson |
| Rony Clanton | Butler |
| Justiin A. Davis | Lester White
(as Justiin Davis) |
| Lucy Gallina | Emily Schroeder |
| Josie Gallina | Emily Schroeder |
| Marceline Hugot | Sister Bernice |
| John Keating | Ernie Moran |
| Heather Lind | Katy |
| Edward Manley | John Wright |
| Edward McGinty | Ward Boss Boyd |
| Rory McTigue | Teddy Schroeder |
| Declan McTigue | Teddy Schroeder |
| Tracy Middendorf | Babbette
(as Tracy Lynn Middendorf) |
| Brady Noon | Tommy Darmody |
| Connor Noon | Tommy Darmody |
| Franklin Ojeda Smith | Deacon Lemuel Cuffy |
| Natalie Wachen | Lenore White |
| Kathryn Avery | Dancer #1 |
| Leslie Flesner | Dancer #2 |
| Kate Harpootlian | Dancer #3 |
| Sarah Skogland | Dancer #4 |
| Emily Tyra | Dancer #5 |
| Jim Dykes | High Roller |
| Ella Jane New | Odette |
| Robyn Young | Floozy |
| Malik J Ali | Church Member
(uncredited) |
| Chris Angerman | Newsboy
(uncredited) |
| Don Arangio | Newsie
(uncredited) |
| Lee Cunningham | Van Alden's Neighbor
(uncredited) |
| Michael Dean | State Investigator
(uncredited) |
| Gray Ellis | Angry Church Member
(uncredited) |
| Paul Jude Letersky | Angry Church Member
(uncredited) |
| Ronald Scott Maestri | Municipal Worker
(uncredited) |
| Raymond Mamrak | Church Patron
(uncredited) |
| Dartel McRae | Church Member
(uncredited) |
| M. Xavier O'Connor | Ritz Elevator Operator
(uncredited) |
| McKenzie Shea | Deuces Girl
(uncredited) |
| Tom Stratford | Townsman
(uncredited) |