A graduate of the University of Oklahoma, Chapman appeared in numerous Broadway shows including Ladies of the Corridor, The Chase, The Traveling Lady, and Marathon '33. His other stage credits included Mister Roberts, The Time of Your Life, and The Glass Menagerie. He also appeared in small roles in hundreds of films and television series.
Chapman was also a playwright; his works The Buffalo Skinner and Cry of the Raindrop were both produced Off-Broadway. In 1973, he became the artistic director of the Group Repertory Theatre in Los Angeles (now called the Lonny Chapman Group Repertory Theatre), which staged over 350 productions.
He is survived by his wife, Erma Dean, and his son Wyley Dean.