[3] Gordon began performing at age three; in his television debut, he won second place on Ted Mack's Amateur Hour singing Johnnie Ray's "Cry".

At 13, Gordon began a career on Broadway as Nick in Herb Gardner's A Thousand Clowns, a role for which he earned a Tony Award nomination.

In the 1970s, Gordon appeared in the Barney Miller spin-off Fish, starring Abe Vigoda, and from 1973 to 1974 was a regular on The New Dick Van Dyke Show.

[citation needed] Primarily as a character actor, Gordon became a familiar face in numerous feature films and television series.

His most notable voice roles were Donatello and Bebop in Teenage Mutant Ninja Turtles, and as Jake "Razor" Clawson in SWAT Kats: The Radical Squadron (1993).

Gordon's voice was also featured in other animated series, mostly Hanna-Barbera shows such as Jabberjaw (as Clamhead), Tarzan, Lord of the Jungle, The Kid Super Power Hour with Shazam!

(as Captain Marvel Jr.), Meatballs & Spaghetti (as bassist Clyde), Pac-Man (as Inky), Mighty Orbots (as Robert Simmons), Pole Position, The Jetsons, The Smurfs, The Adventures of the American Rabbit (as the titular character), Superman, Snorks (as Junior Wetworth), Gravedale High (as Reggie Moonshroud), Space Cats, A Pup Named Scooby-Doo (as Englebert Newton), Darkwing Duck (as Dr. Fossil), Tom & Jerry Kids and its spin-off Droopy, Master Detective, Batman: The Animated Series (as the Penguin's henchman Sheldrake), Aaahh!!!

On April 20, 2022, it was revealed that Gordon would reprise his role as Donatello for the video game, Teenage Mutant Ninja Turtles: Shredder's Revenge.

It continues to be cablecast and webcast live In 2005, Gordon hosted a weekly radio talk show heard on KRLA in Los Angeles, California.

With live streams and podcast archives, the show was notable for featuring nationally known guests, including senators, congressmen, bestselling authors, and entertainment figures.