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, 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 the burly, fair-haired Gavan has managed to get, as well as that of the dashing British officer from Virginia Captain Leroy in Sharpe's Eagle.
Gavan was cast as sadistic killer Dan Suggs in the 1989 miniseries Lonesome Dove.
He appeared in Rich Man, Poor Man and Tales From The Crypt. 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.
