Finding himself broke, he began taking bit parts in as many films as he could, including
The Bride of Frankenstein (1935), and also worked as a stunt man. In the early
1930s, he began appearing in higher quality films and received more substantial roles as his talent was recognized. This culminated with his receiving the very first
Academy Award for Best Supporting Actor for his role as Swan Bostrom in the period film
Come and Get It (1936). Two years later he portrayed town drunk and accused murderer Muff Potter in
The Adventures of Tom Sawyer.
Throughout his career, Brennan was frequently called upon to play characters considerably older than he was in real life. A 1932 accident that cost him many teeth, his rapidly thinning hair, thin build, and raspy voice all made him seem older than he really was. He used these physical features to great effect. In many of his film roles, Brennan wore dentures; in
Northwest Passage -- a film set in the late 18th century, when most people had bad teeth -- he wore a special dental prosthesis which made him appear to have rotting and broken teeth.
Director
Jean Renoir gave the character actor a leading role in
1941; Brennan played the top-billed lead in
Swamp Water, a drama directed by Renoir and featuring
Walter Huston.
In the
1941 Sergeant York, he played a sympathetic preacher and dry goods store owner who advised the title character played by
Gary Cooper. He was particularly skilled in playing the hero's sidekick or as the "grumpy old man" in a picture. Though he was hardly ever cast as the villain, notable exceptions were his roles as Old Man Clanton in the classic 1946 film
My Darling Clementine opposite
Henry Fonda, the 1962
Cinerama production
How the West Was Won as the murderous Colonel Jeb Hawkins, and as
Judge Roy Bean in
The Westerner, for which he won his third best supporting actor Academy Award, in 1940.
In the 1950s, he starred in the
ABC's television series The Real McCoys, which costarred
Richard Crenna, and
Kathleen Nolan. The comedy about a poor
West Virginia family which relocated to a farm in southern California ran on ABC from 1957-1962, before switching to
CBS for a final season as
The McCoys. Brennan appeared in several other movies and television programs, usually as an eccentric "old-timer" or "prospector". He also made a few recordings, the most popular being "Old Rivers", released as a single in 1962 by Liberty Records with "The Epic Ride Of John H. Glenn" on the flip side. Brennan starred as wealthy executive Walter Andrews in the short-lived mid-1960s
television series The Tycoon. In 1967, he starred in the television series
The Guns of Will Sonnett, where he played a man in search of his gunfighter son, James, with his grandson, Jeff, played by
Dack Rambo. After the series went off the air in
1969, Brennan continued working in both television and feature films. He received top billing over
Pat O'Brien in the
TV-movie The Over-the-Hill Gang in
1969 and
Fred Astaire in
The Over-the-Hill Gang Rides Again the following year. From 1970 to 1971, he was a regular on the show
To Rome With Love, which would be his last TV show as a member of the permanent cast.