York made his film debut as Lucentio in Zeffirelli's The Taming of the Shrew (1967), then was cast as Tybalt in Zeffirelli's 1968 film adaptation of Romeo and Juliet with Leonard Whiting and Olivia Hussey. He also starred in an early Merchant Ivory Productions film, The Guru (1969). In Cabaret (1972) York played Brian Roberts, and in 1979 reunited with Zeffirelli as a fiery John the Baptist in Jesus of Nazareth.

York starred as D'Artagnan in the 1973 adaptation of The Three Musketeers. One year later the sequel was released (roughly covering events in the second half of the book) titled The Four Musketeers. These two films are still popular and generally accepted as the best film version of the famous Dumas adventure story.[1] 15 years later, most of the cast (and crew) joined together in a third film titled The Return of the Musketeers based on the Dumas novel Twenty Years After. York had already been on British TV as Jolyon (Jolly) in The Forsyte Saga (1967). He also played the title character in the film adaptation of Logan's Run (1976). He appeared in Jesus of Nazareth as the prophet and cousin of Jesus, John The Baptist on (1977).

Since his auspicious early work, York has enjoyed a busy and varied career in film, television, and on the stage. His Broadway theatre credits include Bent, The Crucible, and the ill-fated musical The Little Prince and the Aviator, which closed during previews. He also has made many sound recordings as a reader, including Harper Audio's production of C.S. Lewis's The Lion, the Witch, and the Wardrobe.

He appeared in the Babylon 5 episode A Late Delivery From Avalon as the mentally disturbed and guilt-ridden David McIntyre, the Earthforce gunner who obeyed his Captain's orders to open fire on a Minbari vessel, which started the war between Minbar and Earth that would ultimately kill over 250,000 humans. He also appeared as Professor Asher Fleming, a 60 year-old Yale professor and boyfriend of Yale student Paris Geller (Liza Weil) in the fourth season of Gilmore Girls. He did the voice of the character Ares in the Justice League Unlimited episode "Hawk & Dove". York stared in both The Omega Code and its sequel, Megiddo: The Omega Code 2, as Stone Alexander, portraying the Antichrist of Christian eschatology.

York also played President Alexander Bourne of Macronesia (formerly New Australia) on seaQuest 2032, a role that was quickly fleshed out and would have remained a major player in the series had it lasted past the thirteen episodes it was ordered for in its third season before ultimately being cancelled. He has played Basil Exposition in all 3 of the Austin Powers movies. He has made an appearance on The Simpsons as Mason Fairbanks, Homer's possible father in Homer's Paternity Coot. He was also in the third season finale of Sliders as a character reminiscent of Dr. Moreau. In 2006, York played the Charles Sobhraj-like character, Bernard Fremont, on Law & Order: Criminal Intent. He has also appeared in Curb Your Enthusiasm.

York also voiced Petrie's uncle Pterano in The Land Before Time VII: The Stone of Cold Fire. It was once rumored that Pterano would return in The Land Before Time XII: The Great Day of the Flyers, but York confirmed that he isn't appearing. York is currently playing King Arthur in a revival of Lerner and Loewe's Camelot, which began its run at the La Mirada Theatre in Southern California, and is on a national tour with hopes of reaching New York.