His other stage roles include Shaw's Saint Joan, and Tiger at the Gates, Christopher Fry's version of a Jean Giraudoux play, which ran 1959–60 on Broadway.

[1] His film roles included a cockney ne'er-do-well in My Fair Lady (1964), Boss Kean in Cool Hand Luke (1967), In Cold Blood (1967) as murder victim Herbert Clutter,[5] John acted as the pilot/flight instructor for Aunt Bee in Season 8 of The Andy Griffith Show, "Aunt Bee's Big Moment"[6] Halls of Anger (1970), Woody Allen's Sleeper (1973), rancher David Braxton in The Missouri Breaks (1976), and Orval in First Blood (1982).

He played Jimmy Tomorrow in John Frankenheimer's American Film Theater movie of The Iceman Cometh (1973), alongside Fredric March, Lee Marvin, Robert Ryan and Jeff Bridges.

McLiam portrayed Ellis Carter, a young man seeking freedom from his domineering brother, in the 1961 episode "The Big Spender" of the television series Window on Main Street.

He had guest roles in dozens of other television series,[7] including The Twilight Zone, Mannix, Magnum, P.I., M*A*S*H, Murder, She Wrote, The A-Team, and Perry Mason.

The central character, played in that production by James Barton, is a father who renounces his faith following the death of his son and spends his savings on partying and loose women before having a heart attack.