| Steve Buscemi | Enoch 'Nucky' Thompson |
| Kelly Macdonald | Margaret Thompson
(credit only) |
| Michael Shannon | Nelson Van Alden |
| Shea Whigham | Elias 'Eli' Thompson |
| Michael Stuhlbarg | Arnold Rothstein |
| Stephen Graham | Al Capone |
| Vincent Piazza | Lucky Luciano
(credit only) |
| Michael Kenneth Williams | Chalky White |
| Anthony Laciura | Eddie Kessler |
| Paul Sparks | Mickey Doyle
(credit only) |
| Jack Huston | Richard Harrow
(credit only) |
| Ron Livingston | Roy Phillips
(credit only) |
| Jeffrey Wright | Valentin Narcisse |
| Gretchen Mol | Gillian Darmody
(credit only) |
| Anatol Yusef | Meyer Lansky |
| Brian Geraghty | Agent Knox |
| Domenick Lombardozzi | Ralph Capone |
| Ben Rosenfield | Willie Thompson |
| Erik LaRay Harvey | Dunn Purnsley |
| Arron Shiver | Dean O'Banion |
| Eric Ladin | J. Edgar Hoover |
| Morgan Spector | Frank Capone |
| Joel Marsh Garland | Stu |
| Margot Bingham | Daughter Maitland |
| David Campbell | Tom (Nucky's Bodyguard) |
| Owen Campbell | Clayton Davies |
| Joe Caniano | Jake Guzik |
| Josh Caras | Henry Gaines |
| Jake Woodbury Davis | Tip |
| Nate Dern | Bureau of Investigation Agent |
| Kayla Ferguson | Doris |
| Maggie Fine | Jerry Flentje's Neighbor in 1-C |
| Rae Gray | Claudia |
| A.J. Heekin | Poker Dealer |
| Will Janowitz | Hymie Weiss |
| Aaron Joshua | Stoop Loudmouth |
| Ned Luke | Boorish Man |
| Shane Nepveu | Flitch |
| Dieter Riesle | Eddie's Friend 1 |
| Eric Reid Schroeder | Tenement Man |
| Christiane Seidel | Sigrid Mueller |
| Dominik Tiefenthaler | Rudy |
| Ben Van Bergen | Thomas |
| Jacob A. Ware | Agent Selby |
| Jonathan Brody | Onyx Club Patron 1 |
| Natalia Lepore Hagan | Onyx Club Patron 2 |
| Amelia Lowe | Onyx Club Patron 3 |
| Clifton Samuels | Onyx Club Patron 4 |
| Brian G. Andersson | Club Patron
(uncredited) |
| Chris Brennan | Onyx Club Patron
(uncredited) |
| Richard R. Corapi | Hospital Patient
(uncredited) |
| Chris Koch | Hotel Guest
(uncredited) |
| Liz Logan | Elegant Harlem Lady #2
(uncredited) |
| Lynsey Leigh Price | Temple Student
(uncredited) |
| Jay Russell | Prosecutor
(uncredited) |
| Romina Schwedler | Onyx Club Dancer
(uncredited) |