"[2] Raised in Phoenix, Arizona, O'Sullivan studied and acted at the University of Denver and the Goodman Memorial Theater in Chicago.
He then played major roles (including a remarkable "prancing" Pandarus in Troilus and Cressida[3]) at the Oregon Shakespeare Festival in 1957 and 1958.
[5] In 1963, he won the Obie and the Laura D'Annunzio Awards for his portrayal of the Director in Pirandello's Six Characters in Search of an Author, directed by William Ball,[2] a role he also performed in London, and in 1965 he performed the title role in Ball's staging of Molière's Tartuffe for the new Repertory Company of Lincoln Center,[6] prompting critic Howard Taubman to praise O'Sullivan for showing "how a Molière performance can be larger than life, and not out of focus... [moving] between cringing, shuffling humility and outrageous arrogance.
"[7] O'Sullivan was a nominee for the Tony Award in 1966 for his role as the villain Sedgwick in the Broadway musical, It's a Bird, It's a Plane, It's Superman.
"[9] In July 1971, Michael O'Sullivan was found dead in his San Francisco apartment at the age of 37, a bottle of sleeping pills by his side.