In a futuristic New York known as New Rome, visionary architect Cesar Catilina dreams of building "Megalopolis," a utopian city that redefines society’s limits. Opposing him is the corrupt Mayor Franklyn Cicero, who clings to power and profit. Between them stands Julia, the mayor’s daughter, whose love for Cesar forces her to choose between loyalty, ambition, and the fate of humanity.
| Cesar Catilina | Adam Driver |
| Mayor Cicero | Giancarlo Esposito |
| Julia Cicero | Nathalie Emmanuel |
| Wow Platinum | Aubrey Plaza |
| Clodio Pulcher | Shia LaBeouf |
| Hamilton Crassus III | Jon Voight |
| Fundi Romaine | Laurence Fishburne |
| Constance Crassus Catilina | Talia Shire |
| Jason Zanderz | Jason Schwartzman |
| Teresa Cicero | Kathryn Hunter |
| Vesta Sweetwater | Grace VanderWaal |
| Clodia Pulcher | Chloe Fineman |
| Charles Cothope | James Remar |
| Commissioner Stanley Hart | D. B. Sweeney |
| Claudine Pulcher | Isabelle Kusman |
| Huey Wilkes | Bailey Coppola |
| Claudette Pulcher | Madeleine Gardella |
| Aram Kazanjian | Balthazar Getty |
| Girl Reporter | Romy Mars |
| Sunny Hope Catilina | Haley Sims |
| Nush 'The Fixer' Berman | Dustin Hoffman |
| Zena The Model | Sonia Ammar |
| Dr. Lyra Shir | Neri Oxman |
| Balin the Fractal | AJ Caba |
| Boy Assassin | Michael Mourra |
| Felix the Butler | Charlie Talbert |
| General | Tommy Lee Driver |
| Cesar's Secretary | Caroline Bloom |
| Bandmaster | George Dillard |
| Ringmaster | Donald Pitts |
| Control Room Engineer | Philip Dido |
| Mrs. Gayle | Gayle Hooker |
| Laughing Man | James Keane |
| TV Newscaster | Sean Hankinson |
| Spanish-Speaking Protester | Andrew Ayala |
| Mr. Singh | Ritwik Chatterjee |
| Servilia | Kendra Stout |
| Non English-Speaking Driver | Max Bojorquez |
| Board Chairwoman | Renee McNeil |
| Wall Street Lawyer | Suzan Norton |
| Wall Street Lawyer | Vince Pasani |
| Elvis Impersonator | Robert Kim |
| Sunny Puppet Dancer | Laura Hawkins |
| Townhouse Guard | Henry Louis Adams Jr. |
| Dance Instructor | Paul Pudney |
| Vesta Lookalike | Vanessa Nichole |
| Vesta Lookalike | Nikki Rush |
| Vesta Lookalike | Tammy Hurtado |
| Fake Vesta in Bed | Emma Anne Wedemeyer |
| Lady Justice Statue | Ivy Lightsey |
| Saw Law Statue | Art Newkirk |
| Mournful Lady Statue | Savannah Powers |
| Jane Doe | Emily Berry |
| Self (archive footage) (uncredited) | Adolf Hitler |
| Self (archive footage) (uncredited) | Benito Mussolini |
| New Rome Citizen (uncredited) | Matt Gulbranson |
