Warden had his first credited film role in Man with My Face in 1951. In 1952, he began a three year stint as the coach in the television series Mr. Peepers. Warden's breakthrough role was his appearance in Twelve Angry Men in 1957.
Warden appeared in over one hundred movies during a career which spanned over 50 years. He received an Emmy Award for his performance as George Halas in Brian's Song (1971), and was nominated for Academy Awards as Best Supporting Actor for his performances in Shampoo (1975) and Heaven Can Wait (1978). Other film credits include Death on the Nile (1978, with Peter Ustinov), Being There (1979, with Peter Sellers), and Problem Child (1990, with John Ritter). One of his last film roles was in The Replacements (2000) as a curmudgeonly football team owner.