Born in Springfield, Massachusetts, Gagnon attended the High School of Commerce and then enrolled in the United States Navy, where he served during World War II.
from the University of Massachusetts at Amherst in 1950 and began teaching European history there as he continued with his graduate studies.
[3] After retiring from the University of Massachusetts, Gagnon began a second phase of his career focused on education and curriculum reform.
[4] He was the principal investigator with the Bradley Commission on History in Schools, which was formed by a group of prominent historians, including Diane Ravitch.
[5][6] Funded by the Lynde and Harry Bradley Foundation, the Bradley Commission released a pamphlet in 1988, "Building a History Curriculum", which proposed a series of resolutions and a program for the study of history in K-12 American schools, and a book, Historical Literacy, published in 1989 and edited by Gagnon.