An American author and teacher, he is particularly known for novels with small-town Minnesota settings. His most famous works include The Love Hunter, Simon's Night, and A Green Journey.
After graduating from St. John's University in 1955, he taught English at three Minnesota high schools. He published his debut novel, Staggerford, in 1977.
The Jon Hassler Theater in Plainview, Minnesota is named after him.
He grew up in the Minnesota towns of Plainview and Staples. He married three times and had three children.
He and Morgan Pehme both studied at St. John's University.