Universal cowboy star Rod Cameron plays Geoffrey, conductor of a high-toned symphony orchestra. Secretly harboring the desire to become a swingin' jazz trumpeter, Geoffrey takes a job at a "hot" Broadway nightclub. Here he meets and falls in love with café songstress Donna (Frances Raeburn), who has led her family to believe that she's studying for a classical-music career. Meanwhile, a comedy-relief romance develops between Geoffrey's snooty valet Chumley (Arthur Treacher) and Donna's best pal Pat (Jacqueline De Wit). For those not interested in the plot (what there is of it), Swing Out, Sister includes specialty numbers by organist Selika Pettiford and the Lou Diamond Quintet.
| Actor | Role |
|---|---|
 Rod CameronGeoffrey Cabot | Geoffrey Cabot |
 Billie BurkeJessica Mariman | Jessica Mariman |
 Arthur TreacherChumley | Chumley |
 Frances RaeburnPenelope Mariman / Donna Leslie | Penelope Mariman / Donna Leslie |
 Jacqueline deWitPat Cameron | Pat Cameron |
 Samuel S. HindsRufus Mariman | Rufus Mariman |
 Fuzzy KnightClutch | Clutch |
 Milburn StoneTim Colby | Tim Colby |
 Edgar DearingMotorcycle Cop | Motorcycle Cop |
 Sam FlintMr. Bradstreet | Mr. Bradstreet |
 Constance PurdyMrs. Bradstreet | Mrs. Bradstreet |
| LLeo DiamondLeo Diamond | Leo Diamond |
| SSelika PettifordOrgan Specialty Act | Organ Specialty Act |
| DDee CarrollHat Check Girl (uncredited) | Hat Check Girl (uncredited) |