Fox began his career in animation at Max Fleischer's studio, but left due to labor unrest. He entered the comic book industry, working for a number of studios and companies, including DC Comics. In 1940, he married Helen Fittipaldi. During this period he was an editor and a cover artist for Quality Comics, with his work gracing the covers of such titles as Torchy and Plastic Man. In 1941, he wrote several weeks of continuity for the Spirit daily newspaper strip. A 1941 comic book written by Gil Fox described the bombing of Pearl Harbor in surprising detail, precisely one month before it happened. He left his editorial position at Quality in 1943 to serve in World War II, where he worked for Stars and Stripes. Once discharged from military service, Fox freelanced for Quality Comics until the early 1950s.
Fox later moved to advertising, working for the Johnstone and Cushingadvertising agency. There he met Dik Browne, and assisted him on Browne's comic strip Hi and Lois. He also assisted/ghosted on several other strips as favors to friends. His daughter, Susan Fox, continued the tradition. She lettered several newspaper strips in the 1970s and 1980s, including Star Hawks, Annie, and Beetle Bailey His daughter, Donna Morency is also an artist. Her works are in collections throughout the United States, Europe and Asia. His wife Helen died in 1998.
^"United States Social Security Death Index," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/JBWR-2WB : accessed 25 Feb 2013), Gilbert T Fox, 15 May 2004; citing U.S. Social Security Administration, Death Master File, database (Alexandria, Virginia: National Technical Information Service, ongoing).