Born in Toronto, Ontario, Granatstein received a graduation diploma from Royal Military College Saint-Jean in 1959, his BA from the Royal Military College of Canada (RMC) in 1961, his MA from the University of Toronto in 1962 and his Ph.D from Duke University in 1966.
Granatstein served in the Canadian Army from 1956 to 1966. After which, he taught at York University until 1996 where he is Distinguished Research Professor of History Emeritus.
Granatstein is an outspoken defender of traditional narrative history in lectures, books, print, and broadcast media. Perhaps his best known work is Who Killed Canadian History?, which expressed his alarm at the widespread ignorance of history among students, and the distortions he complained were perpetrated by a new generation of social historians. He wrote of an ideological war waged inside university history departments:
As the old white males rallied themselves and fought back, the resulting war produced heavy casualties, much bloodshed, and vast expenditures of time and effort. The political historians believed that narrative was important, that chronology mattered, and that the study of the past could not neglect the personalities of the leaders and the nations they lead. The social historians had no interest in the history of the "elites" and almost none in political history, except to denounce repressiveness of Canadian governments and business....Blame had to be allocated. Canada was guilty of genocide against the Indians, the bombing of Germany, the ecological rape of the landscape, and so on. Their aim was to use history, or their version of it, to cure white males of their sense of superiority.
He is the author of over sixty other books, including Yankee Go Home?, Who Killed The Canadian Military?, and Victory 1945 (with Desmond Morton). The Generals won the J.W. Dafoe Prize and the UBC Medal for Canadian Biography. The Last Good War was awarded the Canadian Authors Association's 2005 Lela Common Award for Canadian History.
He was a member of the RMC Board of Governors and is Chair of the Council for Canadian Security in the 21st Century.
Granatstein has also been involved in television coverage of political and military events. On June 6, 1994, he was part of the CBC's coverage of the 50th anniversary of D-Day, as the network's chief correspondent, Peter Mansbridge got expert help in the commentary from Granatstein. Granatstein helped Mansbridge again on May 8, 1995, during the CBC's coverage of the 50th anniversary of VE Day. He reprised the same role on the 60th and 65th anniversaries of D-Day and V-E Day.
In recent years, Granatstein shifted towards the political right. In 2003, he supported Canada's involvement in the Iraq War. He defended his position in Whose War Is It?, a book published in 2007. In this book, Granatstein criticized Lloyd Axworthy's foreign policy while praising positions adopted by Stephen Harper. He also expressed serious reservations about multiculturalism and a disdain for Quebec independence, accusing Lucien Bouchard of being a demagogue and a liar.
Jack Granatstein served as the head of the Canadian War Museum in Ottawa from 1998 to 2001 and was a driving force behind the building of the museum's new home that opened in 2005. He currently sits on the Advisory Council and is a Distinguished Research Fellow at the Canadian Defence and Foreign Affairs Institute.
The Royal Society of Canada awarded him the J.B. Tyrrell Historical Medal (1992) for "outstanding work in the history of Canada". In 1996, the Conference of Defence Associations Institute named him winner of the Vimy Award.
In 1996, he became an Officer of the Order of Canada, and he won the National History Society's Pierre Berton Prize in 2004 and the Organization for the History of Canada's National History Award in 2006. He has received honorary degrees from the University of Western Ontario, the University of Calgary, as well as Memorial University of Newfoundland, McMaster University, Niagara University, and Ryerson University.
Jack Granatstein is a descendant of Mendel Granatstein, a Polish Jew, who emigrated to Toronto,where he became a successful business owner in the textile industry and became the first Jew to own a home in Toronto. The Granatstein house at 42 St. George Street was acquired by the University of Toronto, in 1947, and was demolished to make room for the Bahen Centre, in 1999.