Davis was born in Marion, Indiana, where he grew up on a small farm with his father Jim Sr., his mother Betty, his brother Dave, and 25 cats. His love of cartooning emerged during the time he would normally be doing chores, but couldn't due to asthma.
Prior to creating Garfield, Davis worked for a local advertising agency and later was an assistant on Tom Ryan's comic strip, Tumbleweeds. He then created a comic strip, Gnorm Gnat, that ran for five years in The Pendleton Times, an Indiana newspaper. Devis tried to sell it to a national comic strip syndicate, but was told, "It's funny. But bugs? Who can relate to a bug?" Five years after starting Gnorm Gnat, Davis drew a giant foot that fell out of the sky, crushing Gnorm and ending the comic strip.
He now resides in Muncie, Indiana where he and his staff continue to produce Garfield under his own company, Paws, Inc, which started in 1981. He is married to Carolyn, gifted singer and elementary teacher, and has a son named James.
Ironically, Davis did not have cats when he started Garfield and still does not today. He does, however, have a dog named Molly.