A spot on Lux Radio Theatre in 1947 brought her a screen-test offer from 20th Century Fox.

[7] Castle was discovered by a talent scout at a restaurant in Beverly Hills and signed to a seven-year contract with Universal-International.

[8][9] She appeared in the films Mr. Belvedere Goes to College (1949),[5] Payment on Demand (1951), The Prince Who Was a Thief (1951) Invasion, U.S.A. (1952), Cow Country (1953), 99 River Street (1953), Beginning of the End (1957), and Arrivederci Roma (1957).

In the 1950s, Castle moved into television, with multiple guest roles on Fireside Theater, Cheyenne, 77 Sunset Strip, and The Restless Gun.

In 1957, she played defendant Sally Fenner in the Perry Mason episode, "The Case of the Negligent Nymph".

In 1958, Castle appeared with Jesse White in a production of A Hole in the Head at the Civic Playhouse in Los Angeles.

[2]: 14 In 1960, Castle and Peter Brown (who also was a regular in Lawman) traveled to rodeos, performing as a song-and-dance team.

Castle stressed, "We're very careful not to sing any romantic songs," treating the act more like a brother-sister team.