| Steve Buscemi | Enoch 'Nucky' Thompson |
| Kelly Macdonald | Margaret Thompson /
Mrs. Rohan |
| Michael Shannon | Nelson Van Alden |
| Shea Whigham | Elias 'Eli' Thompson |
| Michael Stuhlbarg | Arnold Rothstein |
| Stephen Graham | Al Capone |
| Vincent Piazza | Lucky Luciano |
| Michael Kenneth Williams | Chalky White |
| Anthony Laciura | Eddie Kessler
(credit only) |
| Paul Sparks | Mickey Doyle |
| Jack Huston | Richard Harrow |
| Ron Livingston | Roy Phillips
(credit only) |
| Jeffrey Wright | Valentin Narcisse |
| Gretchen Mol | Gillian Darmody
(credit only) |
| Patricia Arquette | Sally Wheet |
| Anatol Yusef | Meyer Lansky |
| Brian Geraghty | Agent Warren Knox /
Jim Tolliver |
| Domenick Lombardozzi | Ralph Capone |
| Ben Rosenfield | Willie Thompson |
| Chris Caldovino | Tonino Sandrelli |
| Ivo Nandi | Joe Masseria |
| Greg Antonacci | Johnny Torrio |
| Kevin O'Rourke | Mayor Edward Bader |
| Eric Ladin | J. Edgar Hoover |
| Patch Darragh | Robert Bennett III |
| Vincenzo Amato | Vincenzo Petrucelli |
| Joe Abbate | Pat |
| Gregory Bastien | |
| Steve Beauchamp | Sid - Nucky's Aide |
| Margot Bingham | Daughter Maitland |
| Surya Botofasina | Mr. Coates - Onyx Club Pianist |
| Pearce Bunting | Bill McCoy |
| Tricia Burns | Cicero Prostitute 1 |
| Michael Chenevert | Reporter #2 |
| Justiin A. Davis | Lester White
(as Justiin Davis) |
| Nore Davis | |
| Thomas Endres | Philadelphia Enquirer Reporter |
| Josie Gallina | Emily Schroeder |
| Lucy Gallina | Emily Schroeder |
| Matt Giroveanu | Deputy #1 |
| Emma Holzer | Edith Thompson |
| Joseph Huffman | |
| Stephen Izzi | |
| Christina Jackson | Maybelle White |
| Travis Jacobs | (as Travis Terrell Jacobs) |
| Joseph La Rocca | Vito |
| Kareem M. Lucas | |
| Eden Marryshow | |
| Declan McTigue | Teddy Thompson |
| Rory McTigue | Teddy Thompson |
| Sean Phillips | |
| Adam Ratcliffe | |
| Tyler Rollinson | (as Tyler Jacob Rollinson) |
| Sarah Shankman | |
| Darrell Shipley | Earl |
| Nisi Sturgis | June Thompson |
| Joe Tippett | Cal |
| Jacob A. Ware | Agent Selby |
| Ashlynn Alexander | Capone Prostitute
(uncredited) |
| Giuseppe Ardizzone | Capone Thug #1
(uncredited) |
| Darik Bernard | Narcisse Thug #1
(uncredited) |
| Andrae Paul Cezair | Onyx Club Staff
(uncredited) |
| Joseph Dimartino | Hawthorne Inn Bartender
(uncredited) |
| Liam Ferguson | Sheriff's Deputy
(uncredited) |
| Marcus Garvey | Self
(archive footage) (uncredited) |
| John Francis Hebert | Mayor Bader's Aide
(uncredited) |
| Brian Kealty | Federal Agent
(uncredited) |
| Austin Kennedy | Ladder Boy
(uncredited) |
| Karmen Kluge | Coffee Shop Waitress
(uncredited) |
| Paul Jude Letersky | NJ State Police Officer
(uncredited) |
| Michael Metta | Stock Broker
(uncredited) |
| Rich Petrillo | Still Bootlegger
(uncredited) |
| Dion Sapp | Narcisse Thug
(uncredited) |
| Nate Steinwachs | Federal Agent
(uncredited) |
| Gerard Sullivan | Nucky's Bodyguard
(uncredited) |