Played the lost son "Chuck Cunningham" in the first season of Happy Days (1974). Is actually younger (by about two months) than Ron Howard, who played his "younger" brother on the show. Howard later directed O'Herlihy in a small part in Willow (1988).
Was an avid tennis player in his youth, even becoming the Irish National Tennis Champion.
Often cast as a villain or antagonistic character. Examples of this include his roles in Death Wish 3 (1985) and Superman III (1983). The character Airk from Willow (1988) and Captain Leroy from Sharpe's Eagle are two of the few heroic roles that he has played during his career.
Though principally a movie star, he has contributed to various TV series. British audience will recognize him most as the heroic Captain Leroy in Sharpe's Eagle. Few will forget his comment "Boys, lets load up and do some shootin'".
Attended both Dublin's Trinity College and the Abbey School.