At Baylor University, Hamm was very involved in art. He drew for the Baylor Round-Up every year he attended from 1945-1948. After graduation, he taught commercial art classes at Baylor and would later serve as the Art Department's Interim Chairman.
Hamm wavered between the drawing board and the pulpit for over 20 years, but after drawing some religious editorial cartoons, he found that they were well-received. Hamm decided that this was the way the Lord wanted him to go. He felt that he could reach a much larger congregation with "picture sermons in black and white" than with words. And he was right.
In the 1960's, he and his wife, Dorisnel, founded the syndicate Religious Drawings to distribute his inspirational artwork to newspapers worldwide in order to preach Christianity and further the Gospel. At one point, his cartoons reached a congregation of 29,000,000 readers a week.
He also founded "The Jack Hamm Show," one of the first television art programs, which aired in the Dallas, Houston and Waco, Texas, television markets. He also served as editorial cartoonist for the Baptist Standard of Texas and as instructor and artist-in-residence at Dallas Baptist College.
Hamm authored and illustrated over 25 books, some of which are still in print today. Some of his instructional art books, such as Drawing the Head and Figure, Cartooning the Head and Figure, Drawing Scenery and How to Draw Animals are considered to be classics in the field.
He is widely recognized for his talent as an art instructor, as evidenced by his numerous publications gifted students, and many awards.
Hamm began drawing religious cartoons as a hobby, but soon learned that it was a rewarding business. Eventually, he found a meaningful way to combine his dual passions for art and religion.