After minor uncredited appearances in a pair of 1948 movies, Stone earned his first credit, under the stage name John Fontaine, with a voice role in Cinderella in 1950.
He then appeared in four films released in 1958: The Big Beat, Damn Citizen, The Thing That Couldn't Die and Money, Women and Guns.
In 1954, he starred in the Italian television series, I Tre moschettieri (The Three Musketeers) as D'Artagnan opposite Paul Campbell (as Aramis), Sebastian Cabot (as Porthos), and Domenico Modugno (as Athos).
Individual episodes of the series were merged for release as feature films in European theaters including Knights of the Queen in 1954; The King's Musketeers and La Spada Imbattibile, both released in Europe in 1957; Le Imprese di Una Spada Leggendaria in 1958; and Mantelli Espade Insanguinate in 1959.
Stone's other television credits included roles in Adventures in Paradise, The Outer Limits, The Californians, Johnny Midnight, and Surfside 6.