O'Herlihy was born 29 July 1951 in Dublin, Ireland,^[1] the son of Irish parents, actor Dan O'Herlihy and his wife, Sandymount native Elsie Bennett. He was raised in Malibu, California and Dublin.^[2]

After graduating from Phillips Academy in Massachusetts, he attended Trinity College, Dublin^[2] and as an avid tennis player, he became Irish National Tennis Champion.^[3]

He has over thirty screen credits to his name, most of them in villainous or antagonistic roles such as Never Say Never Again, Superman III,^[2] Death Wish 3 and The Last Outlaw. His role as Airk Thaughbaer in the 1988 fantasy Willow is one of the few heroic roles that he has portrayed, as well as that of the dashing American Loyalist officer from Virginia Captain Leroy in Sharpe's Eagle.

He appeared in Rich Man, Poor Man and Tales From The Crypt.^[4] In 1994, he starred as John Garrideb in "The Mazarin Stone" from Granada TV's Sherlock Holmes series. The events of the story were rewritten and merged with The Adventure of the Three Garridebs.

He was cast as the eldest sibling, Chuck Cunningham, on Happy Days.^[3][5] He played Chuck during season 1 until the episode "Give the Band a Hand" and was replaced for season 2 by Randolph Roberts until the episode "Guess Who's Coming to Christmas". Chuck was not seen again but was later mentioned in a few other episodes ending with "Fish and the Fins". After that, Chuck was written off the show completely with later episodes depicting the Cunningham family with only two children with Richie as the elder. The character gave rise to the pejorative term "Chuck Cunningham Syndrome", referring to characters who disappear from TV shows without an In-Universe explanation and are later retconned to have never existed.^[6] O'Herlihy did not want to become stuck in television roles, preferring films. He played a warrior in the George Lucas production Willow, directed by his Happy Days brother, Ron Howard. He also appeared in the pilot episode of Star Trek: Voyager, "Caretaker", as the Kazon First Maje, Jabin. He also appeared in The Six Million Dollar Man^[3] and The Bionic Woman television series.

O'Herlihy was cast as sadistic killer Dan Suggs in the 1989 miniseries Lonesome Dove.

By the 1990s, O'Herlihy had permanently relocated to the UK, where he preferred to work in the theatre and on television, with roles on British television, including Coded Hostile, Sharpe, Jonathan Creek, and Midsomer Murders.

In 2009, O'Herlihy returned to the big screen as Sheriff Vaines in the follow-up to Neil Marshall's cult horror film, The Descent Part 2, and over a decade later returned to the screen again to play the leading role of writer John Anderson for director Nic Saunders in Queen of the Redwood Mountains, a film inspired by the authors of the Beat Generation, and due for release in 2021.

O'Herlihy had four children. He died in Bath, Somerset, on 15 September 2021, at the age of 70 of undisclosed causes.^[4][7]

• Gavan O'Herlihy at IMDb