Most well known for his work in the late 20th-century films Dante's Peak (as Paul Dreyfus), Going in Style (as Pete), and The Thing (as Norris), Hallahan is also notable for his portrayal of Captain Charles Devane on the NBC series Hunter.
After earning his bachelor's degree from Rutgers University and his Master of Fine Arts degree in Acting from Temple University, he made his screen debut in a PBS Great Performances version of Cyrano de Bergerac.
He enlisted in the United States Navy in the 1960s.
Born to an Irish Catholic family in Philadelphia, Pennsylvania, he grew up with a brother, Kenneth, who became a priest. Charles Hallahan's first marriage was to Elizabeth Widmann; he later married Barbara Gryboski with whom he had two children.
He appeared with Brett Butler in two dozen episodes of the popular sitcom Grace Under Fire.