His first professional onscreen appearance was in a small, uncredited role in the 1961 film The Errand Boy, followed by roles as Barry, a neighborhood kid, in The Adventures of Ozzie & Harriet; on The Dick Van Dyke Show; and as "Arnold Mooney", son of banker Theodore J. Mooney portrayed by Gale Gordon, on The Lucy Show.

In 1964, at the age of ten, he appeared in the ABC medical drama about psychiatry, Breaking Point in the episode titled "A Land More Cruel".

He appeared on the stage as Linus in You're a Good Man Charlie Brown, which he reprised when the musical was adapted for television in 1973.

[6] In October 2011, Barry Livingston released his anecdote-filled autobiography, The Importance of Being Ernie -- detailing his career from My Three Sons to Mad Men and beyond.

Barry Livingston is the only cast member of My Three Sons to still have an active Screen Actors Guild Card.