The young Johnson, renamed "Frankie Darro" (evidently in reference to the child's daring), appeared in his first film at the age of six.

He received good notices for his dramatic ability: "Little Frankie Darro is one of the cleverest child actors on the screen, and he has quite a part in The Signal Tower.

Director Wellman cast him as the lead in Darro's most important role during the 1930s, Wild Boys of the Road, an indictment of teens vagabonding across America during the Depression.

Darro signed instead with producer Maurice Conn of Ambassador Pictures, where he starred in a series of modestly budgeted action features through 1937.

With the play and film Dead End creating a vogue for "tough street kids" stories, Darro signed with Columbia Pictures for two action features, Reformatory and Juvenile Court; he also played a sympathetic role in Columbia's popular serial The Great Adventures of Wild Bill Hickok.

Upon his return to civilian life, Monogram welcomed him back and cast the perennially youthful Darro in its The Teen Agers campus comedies.

As film and TV roles became fewer, Darro opened his own tavern on Santa Monica Boulevard, naming it "Try Later,"[5] after the response he most often received when he asked Central Casting for work.

Frankie Darro is probably best known to modern audiences for two films in which he isn't even seen: Walt Disney's Pinocchio (1940, as the voice of Lampwick), and Forbidden Planet (1956, as one of the actor/operators inside the now iconic 7-foot-tall "Robby the Robot").

He did continue to play small parts well into the 1960s, mostly on television: The Red Skelton Show, Bat Masterson, Have Gun—Will Travel, The Untouchables, Alfred Hitchcock Presents, The Addams Family, and Batman (episodes 9 and 10).