| Steve Buscemi | Enoch 'Nucky' Thompson |
| Kelly Macdonald | Margaret Thompson |
| Michael Shannon | Nelson Van Alden /
George Mueller |
| Shea Whigham | Elias 'Eli' Thompson |
| Michael Stuhlbarg | Arnold Rothstein
(credit only) |
| Stephen Graham | Al Capone
(credit only) |
| Vincent Piazza | Lucky Luciano |
| Michael Kenneth Williams | Chalky White
(credit only) |
| Anthony Laciura | Eddie Kessler |
| Paul Sparks | Mickey Doyle |
| Jack Huston | Richard Harrow |
| Charlie Cox | Owen Sleater |
| Bobby Cannavale | Gyp Rosetti |
| Gretchen Mol | Gillian Darmody |
| Anatol Yusef | Meyer Lansky |
| Meg Steedle | Lillian 'Billie' Kent
(as Meg Chambers Steedle) |
| Patrick Kennedy | Dr. Douglas Mason |
| Kevin O'Rourke | Mayor Edward Bader |
| Victor Verhaeghe | County Treasurer Damien Fleming |
| Michael Cumpsty | Father Ed Brennan |
| John Harrington Bland | Scotty Gulliver - Faraday Irons Manager |
| P.J. Brown | Chicago Prohibition Agent Coughlin
(as PJ Brown) |
| Chris Caldovino | Tonino Sandrelli |
| E.J. Carroll | Sheriff Victor Sickles |
| Joseph DeVito | Masseria's Man #1 |
| Marc D. Donovan | Deputy Ramsey |
| Emily Dorsch | Cornelia Predock |
| Lauren Elder | Madge - Mickey's Date |
| Peter Epstein | Masseria's Man #2 |
| Josie Gallina | Emily Schroeder |
| Lucy Gallina | Emily Schroeder |
| Jenna Gavigan | Evelyn - Artemis Club Girl |
| Mary Grill | Woman at Herkemeyer's Speakeasy |
| Ed Heavey | Nucky's Bodyguard #2 |
| Matt Hobby | Thompson House Servant Phillip |
| James Hosey | Mickey's Alcohol Delivery Boy |
| Mike Houston | Ralph - Faraday Iron Salesman |
| John Little | Bishop Norman |
| Charlotte Maier | Mrs. Landau |
| Declan McTigue | Teddy Thompson |
| Rory McTigue | Teddy Thompson |
| Tracy Middendorf | Babette
(as Tracy Lynn Middendorf) |
| Wade Mylius | Elmer - Faraday Iron Salesman |
| Ned Noyes | Hank - Faraday Iron Salesman |
| Jacqueline Pennewill | Thompson House Maid Lillian |
| Christiane Seidel | Sigrid Mueller |
| John Leonard Thompson | Father Schuck |
| Ryan Woodle | Phil - Faraday Iron Salesman |
| Nick Wyman | Dr. Robert Landau |
| Michael Zegen | Benny Siegel |
| Anne Bergstedt | Gillian's Prostitute
(uncredited) |
| Risa Dorken | Lower Class Girl
(uncredited) |
| Steve Fogelman | Ritz Hotel Doorman
(uncredited) |
| Logan Fry | Guest at Award Ceremony
(uncredited) |
| David Itchkawitz | Upscale Citizen
(uncredited) |
| Paul Jude Letersky | Farraday Iron Salesman
(uncredited) |
| Annika Merkel | Herkemeyer's Speakeasy Patron
(uncredited) |
| Jena Mroz | Gillian's Prostiute
(uncredited) |
| Richie Noodles | Bodyguard
(uncredited) |
| Michael Pitt | James 'Jimmy' Darmody
(archive footage) (uncredited) |
| Miriam Pultro | Artemis Club Girl
(uncredited) |
| Tom Stratford | Gyp's Man
(uncredited) |
| Jim Zunt | Herkemeyer's Speakeasy Patron
(uncredited) |