Mr. Harnick had a career as a performer before he and Charles Hull began TheatreWorks USA in 1961. Its mission was to provide theatrical entertainment for young audiences. Over the years, the company nurtured talents including directors Gabriel Barre, Jerry Zaks, Robert Jess Roth and Michael Mayer; composers Lynn Ahrens and Steven Flaherty, Jason Robert Brown, Larry O'Keefe, Robert Lopez and Jeff Marx; and actors F. Murray Abraham, Roger Bart, Chuck Cooper and John Glover.

During his time at Theatreworks, he produced nearly 100 shows. It is now the nation's largest creator and producer of theatre for young audiences.

Born and raised in the Chicago area, he graduated from the University of Illinois and first started out as an actor. He was a replacement performer in the Broadway premiere of Gentlemen Prefer Blondes and then appeared in the short-lived 1950 revue Alive and Kicking. Another revue, John Murray Anderson's Almanac, came in 1953, followed by Phoenix '55 in 1955.

Jay Harnick did a little bit of everything. He was production stage manager of a Broadway production of Tartuffe in 1965, and produced the Broadway play The Sudden & Accidental Re-Education of Horse Johnson three years later. He was one of the original directors of the American Conservatory Theatre, assisted Jerome Robbins on his American Laboratory Theatre, and directed a vast array of projects, including Mozart's Abduction from the Seraglio at the New York City Opera.

He married actress Barbara Barrie in 1964. Their son Aaron Harnick has become a producer in recent years, with shows like All Shook Up and Martin Short: Fame Becomes Me to his credit. They survive him. He often staged the works of his brother, lyricist Sheldon Harnick, author of Fiddler on the Roof and Fiorello!, at theatres like the Westbury Music Fair. He directed a national tour of Fiddler starring Zero Mostel.

Mr. Harnick stepped down from the artistic directorship of TheatreWorks in 2000.