- Gene Kelly as Donald "Don" Lockwood
- Donald O'Connor as Cosmo Brown
- Debbie Reynolds as Kathy Selden
- Jean Hagen as Lina Lamont. Fresh from her role in The Asphalt Jungle, Hagen read for the part for producer Arthur Freed. She did a dead-on impression of Billie Dawn, Judy Holliday's character from Born Yesterday which won her the role.[5]
- Millard Mitchell as R. F. Simpson. The initials of the fictional head of Monumental Pictures are a reference to producer Arthur Freed. R. F. also uses one of Freed's favorite expressions when he says that he "cannot quite visualize it" and has to see it on film first, referring to the "Broadway Melody" sequence.
- Cyd Charisse as the long-legged woman in the green sequined dress and Louise Brooks–style hair who vamps Gene Kelly in the "Broadway Melody" sequence.
- Douglas Fowley as Roscoe Dexter, the director of Don and Lina's films.
- Rita Moreno as Zelda Zanders, the "Zip Girl" and Lina's friend. As of 2024, Moreno is the last surviving credited star from the film.
Uncredited
- Dawn Addams as "Teresa", a lady-in-waiting to Lina's character in The Duelling Cavalier
- Madge Blake as Dora Bailey, a Hollywood gossip columnist based on Louella Parsons
- Mae Clarke as the hairdresser who puts the finishing touches on Lina Lamont's hairdo
- John Dodsworth as "Baron de la Ma de la Toulon", the villain in The Duelling Cavalier
- King Donovan as Rod, head of the publicity department at Monumental Pictures
- Tommy Farrell as Sid Phillips, the director of the movie featuring "Beautiful Girl"
- Kathleen Freeman as Phoebe Dinsmore, Lina's diction coach
- Stuart Holmes as J. Cumberland Spendrill III, Olga Mara's husband who accompanies her to the premiere of The Royal Rascal
- Judy Landon as Olga Mara, a silent screen vamp who attends the premiere of The Royal Rascal.
- Betty Noyes as the singing voice of Debbie Reynolds on "Would You"[6] and "You Are My Lucky Star"[7]
- In addition, although the film revolves around the idea that Kathy has to dub for Lina's piercing voice, in the scene where Kathy is portrayed recording a line of Lina's dialogue ("Nothing can keep us apart, our love will last 'til the stars turn cold"), Jean Hagen's normal voice is used, because Hagen's deep, rich voice was preferred over Reynolds' somewhat thin and youthful one.[6][7][8]
- Julius Tannen as the man demonstrating the technology of talking pictures[9][10]
- Jimmy Thompson as the singer of "Beautiful Girl"
- Bobby Watson as Don's diction coach during the "Moses Supposes" number
