After acting in the Canadian films "Highpoint" (1979) and "The Kidnapping of the President" (1980), Chaykin made his US debut in "Death Hunt" (1981), but it was a small comedic turn in the hit thriller "WarGames" (1983) that opened Hollywood's eyes to his talent. His towering, glowering performance as the titular not-so-sweet union leader in "Canada's Sweetheart: The Saga of Hal C. Banks" (1986) garnered a Genie Award as Best Actor, as well as a kind of strange stardom in his adopted land. His talent for the outlandish made him right at home in modest-sized but colorful character bits in "The Bedroom Window" (1987) and "Twins" (1988), but it was his especially fine portrayal as the crazed cavalry major who sends Kevin Costner to the frontier before committing suicide in "Dances with Wolves" (1990) that firmly established his reputation as a fine character actor. The following year Chaykin began a collaboration with Canadian director Atom Egoyan in the "En Passant" segment of "Montreal vu par..." and "The Adjuster" (both 1991). In the latter, the actor stood out amidst the superb, eclectic cast as Bubba, a fat, voyeuristic ex-football hero married to an exhibitionist.

Chaykin won a second Genie for his inspired turn in "Whale Music" (1994), playing a child-like musical genius who has retreated from his rock-star life to devote himself to creating a symphonic piece for whales. He proved well-cast as Jessica Tandy's son, a soft core porn movie producer, in 1994's "Camilla" (with Egoyan making an appearance as a film director) and went on to memorable work as a rotund, menacingly depraved politician in "Devil in a Blue Dress" and as one of the crazy uncles in Diane Keaton's "Unstrung Heroes" (both 1995). Under Egoyan's strong direction, Chaykin atypically played a choleric cuckold in "The Sweet Hereafter" before appearing as the owner of the Chez d'Irv diner in "Love and Death on Long Island" (both 1997) and delivering an outstanding turn as a dissipated underworld figure with a monstrous belly in Jon Amiel's "Entrapment" (1999) His role as Nero Wolfe in A&E's "The Golden Spiders: A Nero Wolfe Mystery" (2000) gave him a new pastime, driving constantly by the extraordinary billboard on Sunset Boulevard featuring a "humongous photograph of my face." Chaykin received good notices for his wonderfully petulant portrayal of the detective created by Rex Stout, though some fans of the character thought him too svelte for the part of the 300-pounder.