He had regular roles as Leroy Forrester on The Great Gildersleeve and Julius Abbruzzio on The Phil Harris-Alice Faye Show, as well as continuing as a voice-over artist in animated cartoons, commercials, and spoken-word record albums.

In the late 1950s and early 1960s, Walter would become familiar to a new generation as the voice of Sherman, the nerdy, freckled, bespectacled boy sidekick of time-traveling dog genius Mr. Peabody, in the "Peabody's Improbable History" segments of Jay Ward's Rocky and His Friends (also known as The Bullwinkle Show), which made its debut in 1959.

Tetley worked for Capitol Records in the 1950s, providing an array of juvenile voices for the label's spoken-word and comedy albums, including Stan Freberg Presents the United States of America Volume One: The Early Years (1961).

His Gildersleeve co-star, Harold Peary, had made three albums for Capitol a decade earlier, telling children's stories Gildersleeve-style.

"The Sheriff of Fetterman's Crossing", an episode of Serling's 1965 TV series The Loner, featured guest star Allan Sherman as a character named Walton Peterson Tetley.