In 1965, Leigh collaborated with lyricist Joe Darion and writer Dale Wasserman to write a musical based on Wasserman's 1959 television play, I, Don Quixote. The resulting show, the musical Man of La Mancha opened on Broadway in 1965 and in its original engagement ran for 2,328 performances, and has been revived multiple times. Leigh followed with the showChu Chem, which he also produced, exactly a year after Man of La Mancha, but closed on the road. It finally opened on Broadway in 1989 but ran for only 68 performances. Cry for Us All, based on the play, Hogan's Goat, opened on Broadway in 1970 but ran for 9 performances. Leigh was the producer as well as composer. His musical Home Sweet Homer, starring Yul Brynner, officially opened on Broadway in January 1976 but closed after 1 performance. He produced and wrote the music for Saravà which ran for 101 performances in 1979. Leigh both produced and directed the 1985 revival of The King and I starring Yul Brynner featuring in his final performances as the King of Siam. Lee Adams asked Leigh to collaborate on a musical titled Mike, about producer Mike Todd, but it closed during its pre-Broadway tryout in 1988. After renaming it Ain't Broadway Grand!, the show made it to Broadway in 1993, but lasted 25 performances. He also wrote the musical Halloween with Sidney Michaels, and although Barbara Cook and José Ferrer were in the cast, it did not reach Broadway.
Television
Leigh established Music Makers, Inc., in 1957 as a radio and television commercial production house and was its creative director. His television music included the instrumental music for the ABC Color Logo, the TV commercial jingle "Nobody Doesn't Like Sara Lee", and the Benson & Hedges theme "The Dis-Advantages of You," which reached the Top 40 for The Brass Ring in 1967 and was heard in a series of Benson & Hedges cigarette commercials at that time.
Academic legacy
In 1977, Leigh and others at the Yale School of Music established the Keith Wilson scholarship, to be awarded "to an outstanding major in wind instrument playing." A building in The School of Music at Yale University was named "Abby and Mitch Leigh Hall" in 2001. Leigh later endowed a chair in jazz at Yale University, the Willie Ruff Chair in Jazz, in 2006.
Death
Leigh died in Manhattan on March 16, 2014, from natural causes at the age of 86.
Awards
Leigh won a Tony Award for composing the music for Man of La Mancha. He was also nominated for a Tony Award as the director of the 1985 revival of The King and I. He received the Contemporary Classics Award from the Songwriter's Hall of Fame for "The Impossible Dream."