Born in Boston, Dysart served in the U.S. Air Force and graduated from Emerson College with a degree in speech communications. Though he initially pursued a career in radio, his interest soon turned to acting and he moved to New York, where he landed small roles on television and off-Broadway.
He eventually starred in Broadway shows including The Little Foxes and That Championship Season.
In addition to L.A. Law, Dysart's other film and television credits include Being There, The Thing and Wall Street.
Dysart won an Emmy Award for supporting actor in a drama for L.A. Law in 1992.
He is survived by his wife, a stepson, a brother and two grandchildren.