He began as a child actor using the professional name Donald Keeler playing chubby, beanie-wearing farm boy, Sylvester "Porky" Brockway in the first several seasons (1954–57) of TV's Lassie (retitled Jeff's Collie in syndicated reruns and on DVD).

Vieira borrowed the professional surname from his aunt, Ruby Keeler, star of numerous Warner Bros. musicals in the 1930s.

[1] Other early TV appearances include The Pride of the Family, The Many Loves of Dobie Gillis, Shirley Temple's Storybook, and My Three Sons.

Film appearances include The Private War of Major Benson (1955) with Charlton Heston and The Patriot (2000) with Mel Gibson in which he played as Peter Howard.

In addition to being the nephew of Ruby Keeler, he was the half-brother of actor Ken Weatherwax, best known for portraying Pugsley Addams on the 1960s television sitcom The Addams Family.