Gelbart won Tony Awards for writing the books to the Broadway musical A Funny Thing Happened on the Way to the Forum (with Bert Shevlove) and City of Angels. His other Broadway credits include the plays Sly Fox and Mastergate and the musicals Jerome Robbins' Broadway and The Conquering Hero.
Gelbart was best known for his extensive work in film and television, receiving Oscar nominations for co-authoring the screenplays of Tootsie and Oh, God, and winning the Emmy Award for the TV series M*A*S*H, which he developed. His many other credits include Movie Movie, Blame It On Rio, Barbarians at the Gate, and The Notorious Landlady.
He is survived by his wife, the actress Patricia Marshall, his children, Adam and Becky, and his stepchildren, Gary and Paul.