| Jason Momoa | .... | Arthur |
| Amber Heard | .... | Mera |
| Willem Dafoe | .... | Vulko |
| Patrick Wilson | .... | King Orm |
| Nicole Kidman | .... | Atlanna |
| Dolph Lundgren | .... | King Nereus |
| Yahya Abdul-Mateen II | .... | Manta |
| Temuera Morrison | .... | Tom Curry |
| Ludi Lin | .... | Captain Murk |
| Michael Beach | .... | Jesse (Manta's Father) |
| Randall Park | .... | Dr. Stephen Shin |
| Graham McTavish | .... | King Atlan |
| Leigh Whannell | .... | Cargo Pilot |
| Tainui Kirkwood | .... | Young Arthur (Three Years Old) |
| Tamor Kirkwood | .... | Young Arthur (Three Years Old) |
| Denzel Quirke | .... | Young Arthur (Three Years Old) |
| Kaan Guldur | .... | Young Arthur (Nine Years Old) |
| Otis Dhanji | .... | Young Arthur (Thirteen Years Old) |
| Kekoa Kekumano | .... | Young Arthur (Sixteen Years Old) |
| Julie Andrews | .... | Karathen (Stimme) |
| John Rhys-Davies | .... | Brine King (Stimme) |
| Djimon Hounsou | .... | King Ricou (Stimme) |
| Andrew Crawford | .... | Brine King & King Ricou |
| Sophia Forrest | .... | Fisherman Princess |
| Natalia Safran | .... | Queen Rina |
| Micah D. Ohlman | .... | Newscaster |
| Jack Andrew | .... | Mike (Bully) |
| Frankie Creagh-Leslie | .... | Matt (Bully) |
| Sophia Emberson-Bain | .... | Tour Guide (Aquarium) |
| Ilya Melnikoff | .... | Submarine Captain |
| Hank Amos | .... | Submarine Pirate |
| Kyryl Koltsov | .... | Submarine Crew Member |
| Patrick Cox | .... | Cue Ball |
| Luke Owen | .... | Biker |
| Robert Longstreet | .... | Professor James |
| Devika Parikh | .... | Newscaster Morgan |
| Sonny Le | .... | Metalsmith |
| Jon Fabian | .... | Italian Vendor |
| Mabel Tamone | .... | Italian Young Girl |
| Rita Dinardo | .... | Italian Old Woman |
| Anthony Standish | .... | Barfly |
| Nicoletta Bianca | .... | Italian Mother |
| Victor Leto | .... | Flower Stall Vendor |
| Vincent B. Gorce | .... | Italian Bell Father |
| Gabriella Petkova | .... | Italian Bell Girl |
| Oriana Iacono | .... | Italian Bell Mother |
| Pearl Alice Grantham | .... | Ancient Atlantean Woman |
| Noa Tsuchiya | .... | Ancient Atlantean Child |
| Alice Lanesbury | .... | Arthur's Teacher |
| Nicolas Bosc | .... | Atlantean Soldier #1 |
| Joshua Levinson | .... | Atlantean Soldier #2 |
| Patrick Atchison | .... | Russian Submariner / Ancient Atlantean / Beachgoer (uncredited) |
| Kalani Bell | .... | Arthur's Class at Aquarium (uncredited) |
| Will Bergman | .... | Village Mayor (uncredited) |
| Brendan Byrne | .... | Beachgoer (uncredited) |
| Leo Castro | .... | Italian Fish Monger (uncredited) |
| Harry Cummins | .... | Beachgoer (uncredited) |
| Sasha Dulics | .... | Waiter (uncredited) |
| Andy Esho | .... | Sicilian Villager (uncredited) |
| John Gettier | .... | Submarine Crew (uncredited) |
| Daniel Goodwin | .... | Russian Submariner (uncredited) |
| Bailey Hendy | .... | Atlantean Warrior (uncredited) |
| Tahlia Jade Holt | .... | Atlantean (uncredited) |
| Lane Howson | .... | Beach Goer (uncredited) |
| Wayne Huang | .... | Modern Atlantean (uncredited) |
| Beau Jones | .... | Fisherman (uncredited) |
| Ross Kernahan | .... | Ancient Atlantean (uncredited) |
| Braden Lewis | .... | Beachgoer (uncredited) |
| Jordan Lewis | .... | Ancient Atlantean (uncredited) |
| Niam Mayes | .... | Tourist (uncredited) |
| Salvatore Merenda | .... | Bar Patron (uncredited) |
| Marco Minici | .... | Delivery Man (uncredited) |
| Sam Monaghan | .... | Russian (uncredited) |
| Rhianna Palmer | .... | Bar Patron (uncredited) |
| Kai Pantano | .... | Commando (uncredited) |
| Anna Patch | .... | Atlantean (uncredited) |
| Sam Price | .... | Atlantean (uncredited) |
| Jon Quested | .... | Russian Sailor (uncredited) |
| Jon Reigle | .... | Atlantean (uncredited) |
| Bella Rose | .... | Arthur's Class at Aquarium (uncredited) |
| Thomas Sebecke | .... | Russian Submariner (uncredited) |
| Bobby Silva | .... | Modern Atlantean (uncredited) |
| Rafael Torrijos | .... | Beach Goer (uncredited) |
| Mikey Wulff | .... | Ancient Atlantean (uncredited) |
| Connor Zegenhagen | .... | Russian Submariner #2 (uncredited) |