Kiel made his acting debut in the Laramie episode "Street of Hate". He also acted in an unaired TV pilot featuring Lee Falk's superhero The Phantom, where Kiel portrayed an assassin called Big Mike.
Before film and television, Kiel worked in numerous jobs, including a nightclub bouncer and a cemetery plot salesman.
Kiel broke into films in the early 1960s with Eegah (1962), which was later featured on Elvira's Movie Macabre and Mystery Science Theater 3000, as were The Phantom Planet and The Human Duplicators. He also produced, co-wrote, and starred in The Giant of Thunder Mountain. Kiel appeared as the towering — and lethal — assistant Voltaire to Dr. Miguelito Loveless in first-season episodes of The Wild, Wild West. He later appeared in the episode "The Night of the Simian Terror" as Dimas, the outcast son of a wealthy family, banished because of birth defects that distorted his body and apparently affected his mind. This episode is significant because it allowed Kiel the opportunity to really act rather than just look intimidating. Kiel also had a cameo role in a 1961 episode of The Rifleman.
From 1963 to 1965, Kiel worked as a night school math instructor in Burbank, California.
In the Man from U.N.C.L.E. episode "The Vulcan Affair", Kiel appeared as a guard in Vulcan's plant, and he portrayed Merry in "The Hong Kong Shilling Affair". In 1967 he played a monster in an episode of The Monkees ("I was a Teenage Monster").
Arnold Schwarzenegger and Kiel were the original choices to portray the title character in The Incredible Hulk. Schwarzenegger was turned down due to his height. Kiel participated in the filming of the pilot. During the shoot, producers decided their Hulk needed to be muscular rather than just towering, and Kiel was dismissed because he possessed more body fat than the producers deemed necessary. According to a Den of Geek interview, Kiel, who saw properly out of only one eye, also reacted badly to the contact lenses used for the role, and found the green makeup difficult to remove, so he did not mind losing the part. All recognizable footage of Kiel was cut, except one scene where the Hulk saves the little girl from drowning; the scenes were then reshot with Lou Ferrigno.
He appeared on many other television episodes, such as Laramie, I Dream of Jeannie, Honey West, Gilligan's Island, The Monkees, Daniel Boone, Emergency!, Starsky & Hutch, Land of the Lost, The Fall Guy, and Simon & Simon, and "Kolchak: The Night Stalker".
The James Bond-film producers spotted Kiel in Barbary Coast, and thought he was ideal for the role of Jaws in The Spy Who Loved Me (1977). He was one of the few Bond-villains to appear in two Bond-films, later appearing in Moonraker (1979). He reprised his role of Jaws in the video game called James Bond 007: Everything or Nothing, supplying his voice and likeness. Prior to becoming Jaws, Kiel gave a similarly menacing performance as another metal-toothed villain, Reace, in Silver Streak (1976).
While Kiel's roles as Jaws and Reace offered him little dialogue, his role in Happy Gilmore (1996) was quite the opposite. As Mr. Larson, Happy Gilmore's former employer, Kiel exchanges several one-liners with both Adam Sandler's Happy and Christopher McDonald's Shooter. Kiel took a quieter profile after Happy Gilmore's release, but left semi-retirement to record a role for Tangled (2010). In the acclaimed animated Disney film, he portrayed Vlad, a surprisingly soft-hearted thug who collects ceramic unicorns.
Kiel's IMDb page indicates that he filmed a role for Gary T. Smith's indie film The Engagement Ring, although no production update has occurred since Kiel's passing.
Kiel was born in Detroit, Michigan. His height and features were a result of a hormonal condition known as acromegaly. In his prime, Kiel was 7 ft 1 1⁄2 in (217 cm) tall. He noted in his 2002 autobiography Making It Big in the Movies that he used to state that he was 7 ft 2 in (218 cm), because it was easier to remember. He suffered from acrophobia (fear of heights), and during the cable car stunt scenes in Moonraker, a stunt double was used because Kiel refused to be filmed on the top of a cable car over 2,000 feet (610 m) above the ground.
In 1992, Kiel suffered a severe head injury in a car accident, which affected his balance. He was subsequently forced to walk with a cane to support himself (as shown in his appearance in Happy Gilmore, where he is seen leaning on a person or a cane). Later, Kiel used a scooter or wheelchair.
After his first marriage ended in divorce, Kiel was married to Diane Rogers for 40 years, and at the time of his death, had four children, and nine grandchildren. He co-authored a biography of the abolitionist Cassius Marcellus Clay called Kentucky Lion. Kiel was also a born-again Christian. His website states that his religious conversion helped him to overcome alcoholism.
On September 10, 2014, three days short of his 75th birthday, Kiel died at St. Agnes Medical Center in Fresno, California, of a heart attack, possibly caused by coronary artery disease.