Going up the walls doing somersaults, that trick took a couple of days.

O'Connor appeared in the short-lived Bring Back Birdie on Broadway in 1981 and continued to make film and television appearances into the 1990s including the Robin Williams film Toys as the president of a toy-making company. He died from complications of heart failure on September 27 2003 at age 78 at the Motion Picture & Television Country House and Hospital in Woodland Hills California. His remains were cremated and buried at the Forest Lawn–Hollywood Hills Cemetery in Los Angeles.

He is best known today for his role as Gene Kelly's friend and colleague Cosmo Brown in Singin' in the Rain (1952).