He has appeared in many theater productions, films, and on television since the 1960s
and is known for portraying Dr. Emmett "Doc" Brown in the Back to the Future trilogy (1985–1990) and Jim Ignatowski in the comedy series Taxi (1978–1983), winning two Emmy Awards for the latter.
Lloyd came to public attention in Northeastern theater productions during the 1960s and early 1970s, earning Drama Desk and Obie awards for his work.
He made his cinematic debut in One Flew Over the Cuckoo's Nest (1975), and his television debut in The Adams Chronicles the following year.
Lloyd also starred as Commander Kruge in Star Trek III: The Search for Spock (1984), Professor Plum in Clue (1985), Judge Doom in Who Framed Roger Rabbit (1988), and Uncle Fester in The Addams Family (1991) and its sequel Addams Family Values (1993).
Lloyd earned a third Emmy for his 1992 guest appearance as Alistair Dimple in Road to Avonlea (1992), and won an Independent Spirit Award for his performance in Twenty Bucks (1993).
Lloyd has also been nominated for two Saturn Awards and a BIFA Award.