He studied to become a Jesuit priest, but decided he would rather work with children after having jobs at orphanages and daycare centers. In 1973, he received a Master of Education in Child Studies from Tufts University. In 1975, he moved to Canada to work at the preschool at the University of Guelph in Guelph, Ontario. He also taught in the Department of Family Studies at the University of Guelph as a lecturer and as an assistant professor. In Guelph, he was encouraged to publish the many stories he made up for the children he worked with.
One of Munsch's best-known books, Love You Forever, was listed fourth on the 2001 Publishers Weekly All-Time Best selling Children's Books list for paperbacks at 6,970,000 copies (not including the 1,049,000 hardcover copies).