Born William Gomberg in Cleveland, Ohio, Gilbert's proclivity for creating gags emerged as the humor writer for the Glenville High School Torch on which he worked alongside future playwright Jerome Lawrence and the creators of Superman, Jerry Siegel and Joe Shuster.
There he discovered that his physician, Jack Weinstock, had a skill for writing, and soon the two were contributing sketch comedy to night-club performers including Kaye Ballard and Eileen Barton, and then to the Broadway review Tickets Please.
They worked extensively in early television, particularly the children's programs Howdy Doody and Tom Corbett, Space Cadet, although they also sold material to such mainstream performers as Jackie Gleason.
Later, Gilbert and Weinstock wrote the books for Hot Spot, which starred Judy Holliday, and Catch Me If You Can, a murder mystery based on a French play by Robert Thomas.
In the 1970s, Gilbert returned to children's television, writing gags for Yogi Bear, Scooby-Doo and other Hanna-Barbera characters.