By 1944 he was established as a Broadway juvenile, and he was recruited by Casey Robinson of RKO Radio Pictures to play a sensitive Russian soldier in the film Days of Glory.

Signed to a term contract, Vernon went on to play featured roles in dramas, comedies, and musicals, among them Youth Runs Wild, Step Lively,Those Endearing Young Charms, Bedlam, Riverboat Rhythm, and The Woman on the Beach.

In 1950, now billed as "Glen Vernon," he was a song-and-dance man in the vaudeville revue Hollywood Varieties and played a drunken wastrel in Lucky Losers with The Bowery Boys.

One of his fellow players from Ding Dong Williams, Tommy Noonan, remembered Vernon's calm screen demeanor and cast him as an Army chaplain in his 1959 production The Rookie.

In the 1980s and 1990s, Vernon was cast as quaint old men, in films (So I Married an Axe Murderer) and television (Doogie Howser, M.D.,The Golden Girls).