Mr. Lynch began his training with Herbert Bergoff and Uta Hagen at H.B. Studios in New York's Greenwich Village, and later went on to train extensively with Lee Strasberg at Carnegie Hall. In 1970 be became a lifetime member of the Actors Studio and spent years in the NY theater community playing in dozens of on- and off-Broadway productions. The more notable plays were: The Basic Training of Pavlo Hummel, The Lion in Winter, The Devils, The Lady from the Sea, Action, Live Like Pigs, Richard III, Off on a Tangerine, A View from the Bridge, The Man with The Flower In His Mouth, and Shelly Winters' One Night Stands of a Noisy Passenger.
He made his film debut in the 1973 film c Scarecrow, winner of the Grand Prix Award at the Cannes Film Festival. His performance in Scarecrow launched his film career and took him to Hollywood, where he worked in film and television for over twenty years. His more prominent film work included: Scarecrow, The Seven Ups, Open Season, The Formula, Little Nikita, Invasion U.S.A., Bad Dreams, Dostoyevsky's Crime and Punishment, and William Peter Blatty's The Ninth Configuration. His performance as the evil King Cromwell, in the successful fantasy film The Sword and The Sorcerer, won him the Saturn Award for Best Actor from the Academy of Science Fiction and Fantasy. He also starred in numerous T.V. shows and Movies of the Week, such as Alcatraz: The Whole Shocking Story, Sizzle, Vampire, and Star Trek: The Next Generation's two-part episode "Gambit I / Gambit II."
His work in a variety of indy films earned him a high profile internationally. He played in the first joint production between the Screen Actors' Guild and the People's Republic of China, The Korean Project.
His distinctive scarred appearance was the result of his setting himself on fire during an LSD trip in Central Park, NYC in 1967.