Munsch was born on June 11, 1945 in Pittsburgh, Pennsylvania. He graduated with degrees in history and anthropology and studied to become a Jesuit priest, but decided he would rather work with children after jobs at orphanages and daycare centres. In 1975 he moved to Canada to work at the preschool at the University of Guelph in Guelph, Ontario. In Guelph he was encouraged to publish the many stories he made up for the children he worked with.
His stories do not have a recurring single character. Instead the characters are based on the children to whom he first told the story (including his children). He often performs at children's festivals and appears at elementary schools, sometimes unannounced. He is a bestselling author in both the United States and Canada, and has sold over 30 million books, more than any other Canadian author. In 1999 he became a member of the Order of Canada.