Was originally hired to play Arthur Adamson in Alfred Hitchcock's final film, Family Plot (1976), but Hitchcock had always wanted William Devane for the part. Devane was originally unavailable, so Hitchcock began filming with Thinnes in the role. When Devane became suddenly available one month into filming, Hitchcock unceremoniously fired Thinnes without explanation and replaced him with Devane (Hitchcock later claimed he was dissatisfied with Thinnes' performance). The way Hitchcock handled the firing led to a famously public confrontation between the two men in a crowded Chasen's Restaurant. Thinnes can be seen in several publicity stills from the production, but no footage apparently exists.
Best known as architect David Vincent in the 1960s cult television series, The Invaders (1967). He appeared in a mini-series remake of that series, The Invaders (1995), also in the role of David Vincent.
Served a hitch in the US Army as a Military Policeman.
He made guest appearances on both of the longest running prime time dramas in US television history: Gunsmoke (1955) and Law & Order (1990).
He was considered for the role of Tom Hagen in The Godfather (1972) before Robert Duvall was cast.