In 1951, Mann co-founded Circle in Square Theatre in Greenwich Village, and continued to produce work for the company for five decades, including such landmark plays as Summer and Smoke, The Iceman Cometh, and Long Day's Journey Into Night, which played for nearly 400 performances at the old Helen Hayes Theater.
He remained the owner of the Broadway Circle in the Square Theatre, which houses the current revival of Godspell.
He received the 1957 Tony Award for Best Play for Long Day's Journey Into Night, a 1976 Special Tony Award acknowledging 25 continuous years of quality productions at Circle in the Square, as well as 12 additional Tony Award nominations and seven Drama Desk Awards.
Mann also produced and directed numerous works on other stages, including The Turn of the Screw at New York City Opera and The Night of the Iguana at Moscow's Maly Theater.
In 1963, he founded Circle in the Square Theatre School, a program for training young actors for careers as professionals in theater, television and film.
In November 2007, Applause Books published Mann's memoir, Journeys In The Night: Creating a New American Theatre with Circle In The Square.
He is survived by his two sons, Andrew and Jonathan, and five grandchildren.