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 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? but 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.
- Who Killed Canadian History?, a book arguing that national history has become too splintered for the nation's good, published in 1998
- Whose War Is It?, a book critiquing Canadian foreign policy and defense published in 2007
- Who Killed the Canadian Military?, a book critiquing the Canadian military published in 2004
- Canada's War: The Politics of the Mackenzie King Government, 1939-1945, a book that discussed the political maneuvers of the King government during World War II
- The Ottawa Men: The Civil Service Mandarins, 1935-1957, a book examining the development of the federal civil service and its contribution to Canada's coming of age as a nation
- 4237 Dr. Adrian Preston & Peter Dennis (Edited) "Swords and Covenants" Rowman And Littlefield, London. Croom Helm. 1976.
- H16511 Dr. Richard Arthur Preston "To Serve Canada: A History of the Royal Military College of Canada" 1997 Toronto, University of Toronto Press, 1969.
- H16511 Dr. Richard Arthur Preston "Canada's RMC - A History of Royal Military College" Second Edition 1982
- H16511 Dr. Richard Preston "R.M.C. and Kingston: The effect of imperial and military influences on a Canadian community" 1968 Kingston, Ontario.
- H1877 R. Guy C. Smith (editor) "As You Were! Ex-Cadets Remember". In 2 Volumes. Volume I: 1876-1918. Volume II: 1919-1984. RMC. Kingston, Ontario. The R.M.C. Club of Canada. 1984