Shipman grew up in Salinas, California and is a self-taught artist. His interest in comics and art first began at a young age, while in the sixth grade.
Shipman, with wife Rhoda Shipman, first created the independently produced comic book series Pakkins' Land in 1995, both plotting out the stories together and Gary scripting, lettering, penciling, and inking the illustrations for the series. Pakkins’ Land tells the adventuresome and engaging tale of Paul, a young boy who finds himself in a magical world filled with talking animals, mystery and excitement. Pakkins’ Land has been heralded for excellence by both critics and peers alike, accumulating an international following and numerous award nominations.
Certain characters in the Pakkins' Land stories are named after Shipman's children.
Shipman resides in Illinois with his family and, at times, makes appearances as a guest artist at comic conventions in the region.