John Marshall sold his first cartoon to Parade magazine at the age of 14. After graduating from the Ringling School of Art in Sarasota, Florida, in 1976, he worked as an art director for an advertising agency in Binghamton. He eventually turned to freelance cartooning and among his clients were IBM and GE. In 1982 he created his syndicated comic strip 'Buford'. Between 1989 and 2003 he regularly published cartoons in the Binghamton Press and the San Bulletin. From 1994 to 2000 he worked with Mark Cullum on the comic strip 'Walnut Cove' for King Features Syndicate. Marshall became Denis Lebrun's assistant on 'Blondie' in December 2002, and he became the strip's lead artist in May 2005.