His first screenplay (based on his teleplay The Murder of a Sand Flea) was for the 1957 film, The D.I.,[3] which starred Jack Webb as a Marine Corps drill instructor at MCRD Parris Island.

[5][6] Barrett, along with Peter Udell and Phillip Rose won the 1975 Tony Award for Best Book of a Musical for Shenandoah,[7] which was based on his 1965 film by the same name, which starred James Stewart.

Other notable works written or co-written by Barrett include the 1965 epic film The Greatest Story Ever Told, Smokey and the Bandit, The Green Berets, Bandolero!

Barrett also scripted a made-for-TV remake of The Defiant Ones (which starred Carl Weathers and Robert Urich in the Sidney Poitier and Tony Curtis roles), and adapted the 1967 movie In the Heat of the Night for a weekly series.

(The show starred Carroll O'Connor and Howard Rollins, in the Rod Steiger and Sidney Poitier roles.)