The Maine native began his acting career after completing studies at Boston's Emerson College. He headed to New York in the mid-1950s where he began working off-Broadway in such celebrated productions as "The Quare Fellow" (1958), "Our Town" (1959) and "Six Characters in Search of an Author" (1963). He appeared on Broadway in "A Man For All Seasons", the 1967 revival of "The Little Foxes" and "That Championship Season" in 1972.
Dysart made his feature debut in Richard Lester's stylish drama "Petulia" (1968), one of that decade's best received films. He then donned a stethoscope to play a bungling doctor in Arthur Hiller's comedy "The Hospital" (1971), a pompous surgeon in the sci-fi thriller "The Terminal Man" (1974), and a suspicious physician in Hal Ashby's satirical "Being There" (1979).
On the small screen, Dysart has also worked steadily. Highlights of two decades of TV appearances include playing a slaveowner in "The Autobiography of Miss Jane Pittman" (1974), and playing movie moguls Jack Warner, in the bio film "Bogie" (1980), and Louis B. Mayer, in "Malice in Wonderland" (1985). Dysart has also impersonated several US Presidents, from Ulysses S. Grant in "The Court-Martial of General Custer" (1977) to Dwight D. Eisenhower in "The Last Days Of Patton" (1986). All of these parts seemed to serve as a warm-up for his long-running role in "L.A. Law", a part that earned him an Emmy as Best Supporting Actor.