Clive Barnes of the New York Times designated O'Sullivan as "one of America's best young actors." Raised in Phoenix, AZ, O'Sullivan studied and acted at the University of Denver and the Goodman Memorial Theater in Chicago, then played major roles (including a remarkable "prancing" Pandarus in Troilus and Cressida) at the Oregon Shakespeare Festival in 1957 and 1958.
He was one of a ten actor corps hired by the San Francisco Actor's Workshop under a 1960 Ford Foundation grant to the company, and he came to national prominence with his portrayal of the title role in the Workshop's 1961 King Lear as a "preening, deranged, screeching Lear, imbued with primordial divinity," under Herbert Blau's direction. between cringing, shuffling humility and outrageous arrogance."
His last New York appearance was in 1969 in Georges Feydeau's A Flea in Her Ear with the American Conservatory Theater at the ANTA Theater, and Clive Barnes said of that performance, "zany... galvanic lunacy... this is great farce acting."
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. It is not known whether his death was accidental or a suicide. At the University of Denver
Reverend Paris in The Crucible
Lighthouse Inspector in Thunder Rock
Oedipus in Oedipus Rex
Prometheus in Prometheus Bound
Mephistopheles in Faust, (awarded "Best Actor of the Season")
The Goodman Memorial Theater, Chicago
Beggar in Electra
Prospector in The Madwoman of Chaillot
The Oregon Shakespeare Festival 1957
Panthino in The Two Gentlemen of Verona
Ceremon in Pericles
Brabantio in Othello
Cardinal Wolsey in Henry VIII
Corin in As You Like It
The Oregon Shakespeare Festival 1958
Pandarus in Troilus and Cressida
Antonio in Much Ado About Nothing
Old Gobbo in The Merchant of Venice
Actor's Workshop 1958 - 61
Priam in Tiger at the Gates
Nagg in Endgame
Shanaar in Cock-a-Doodle Dandy
Old Writer in Saint's Day
Subtle in The Alchemist
Patch Riley in A Touch of the Poet
Grandfather in Twinkling of an Eye
Lear in King Lear
New York
Thomas Jefferson, et al. in In White America,1963 Sheridan Square Playhouse
Tartuffe in Tartuffe, 1965, ANTA
Stanford University Repertory Company, 1966–67
(He appeared "in Shakespeare in San Diego")
Six roles in repertory for Stanford Rep
New York return
Malvolio in Love at Let Love (Musical based onTwelfth Night), 1968
Count Alexei in The Bench, by N. R. Teitel, 1968, Gramercy Arts Theater
Camille Chandel in A Flea in Her Ear, 1969, American Conservatory Theater of San Francisco at ANTA, New York.
