| 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
(credit only) |
| Stephen Graham | Al Capone |
| Vincent Piazza | Lucky Luciano
(credit only) |
| Michael Kenneth Williams | Chalky White |
| Anthony Laciura | Eddie Kessler |
| Paul Sparks | Mickey Doyle |
| Jack Huston | Richard Harrow |
| Ron Livingston | Roy Phillips
(credit only) |
| Jeffrey Wright | Valentin Narcisse |
| Gretchen Mol | Gillian Darmody
(credit only) |
| Stephen Root | Gaston Means |
| Brian Geraghty | Agent Knox |
| Domenick Lombardozzi | Ralph Capone |
| Erik LaRay Harvey | Dunn Purnsley |
| Peter McRobbie | Frederick Elliot |
| Kevin O'Rourke | Edward Bader |
| Eric Ladin | J. Edgar Hoover |
| Arron Shiver | Dean O'Banion |
| Morgan Spector | Frank Capone |
| Ty Robinson | Samuel Crawford
(as Ty Michael Robinson) |
| Sean Cullen | Carl Billings |
| Kwabena Ampofo | |
| Jo Armeniox | Alma Pastor |
| Munro M. Bonnell | |
| Nore Davis | |
| Ross Degraw | |
| Thomas Endres | Philadelphia Enquirer Reporter |
| DeWitt Fleming Jr. | Tap Dancer 1 |
| Karida Griffith | Onyx Club Dancer 4 |
| Jared Grimes | Tap Dancer 2 |
| Afra Hines | Onyx Club Dancer 5 |
| Christina Jackson | Maybelle White |
| Peter Francis James | Oliver Crawford |
| Will Janowitz | Hymie Weiss |
| Stephen Paul Johnson | Dolph Liebling |
| Rick Kain | Ira Carroll |
| Thaddeus McCants | |
| Ed Moran | Agent Pearl |
| Celestine Rae | Onyx Club Dancer 11 |
| Allen Lewis Rickman | George Baxter |
| Leajato Amara Robinson | (as Leajato Robinson) |
| G. Michelle Robinson | Mrs.Crawford |
| Christiane Seidel | Sigrid Mueller |
| Natalie Wachen | Lenore White |
| Katherine Waterston | Emma Harrow |
| Noel Wilson | Ward Boss 2 |
| Chloe Arnold | Onyx Club Dancer 1 |
| Maud Arnold | Onyx Club Dancer 2 |
| Jennifer Bowles | Dancer |
| Jonathan Brody | Reporter |
| Brittany Engel-Adams | Onyx Club Dancer 3 |
| Nicole J. Johnson | Onyx Club Dancer 6 |
| Jennifer Jones | Onyx Club Dancer 7 |
| Natalia Lepore Hagan | Onyx Club Patron |
| Amelia Lowe | Onyx Club Patron |
| Marla McReynolds | Onyx Club Dancer 8 |
| Erin Moore | Onyx Club Dancer 9 |
| Jae Ponder | Onyx Club Dancer 10 |
| Jennifer Rias | Onyx Club Dancer 12 |
| Clifton Samuels | Onyx Club Patron |
| Jeffrey Scott Stevens | Onyx Club Patron |
| Brian G. Andersson | Upscale Club Patron
(uncredited) |
| Giuseppe Ardizzone | Capone Leg Breaker
(uncredited) |
| Bruce Conner | Mayor's Assistant Nick
(uncredited) |
| Christian Delevante | Richard Harrow Imposter
(uncredited) |
| Noah Forrest | Capone Thug
(uncredited) |
| Frank L. Messina | Frankie
(uncredited) |
| Rich Petrillo | Capone Legbreaker
(uncredited) |
| Jon Douglas Rainey | Al Capone's Henchman
(uncredited) |
| Kathleen Hope Reilly | Cream - George Baxter's Girlfriend
(uncredited) |