Simpson was born in New York and moved to Canada when he was 10 years old. He was educated at the University of Toronto Schools. He graduated from Queen's University in 1971 in History and Political Science. While at Queen's he worked for the campus radio station CFRC. He won the University's Tricolour Award in his graduating year. He then went on to the London School of Economics. In 1972—1973, he worked as a Parliamentary Intern in Ottawa where he worked for Ed Broadbent. A year later, he joined The Globe and Mail newspaper.

His ongoing career with the Globe began at City Hall in Toronto and with coverage of Quebec politics. In 1977, he became a member of the paper's Ottawa bureau, and eighteen months later he was named The Globe and Mail's Ottawa bureau chief. From 1981–1983, Simpson served as The Globe and Mail's European correspondent based in London. Since January, 1984 he has written a critically-acclaimed daily column on national affairs.

He has written numerous magazine articles for such publications as Saturday Night, Report on Business Magazine, the Journal of Canadian Studies and Queen's Quarterly. He has spoken at dozens of major conferences in Canada and internationally on a variety of domestic and international issues.

Mr. Simpson is a frequent and enthusiastic participant in regular political debate on radio or television, in French and in English. He has been a guest lecturer at such universities as Oxford, Edinburgh, Harvard, Princeton, Brigham Young, Johns Hopkins, Maine, California plus more than a dozen universities in Canada.

In 1993—1994, Simpson was on leave from his column as a John S. Knight fellow at Stanford University in Palo Alto, California. He has been a Skelton-Clark fellow and Brockington Visitor at Queen's University. He has also been a John V. Clyne fellow at the University of British Columbia, a distinguished visitor at the University of Alberta and a member of the Georgetown University Leadership Seminar. He has been awarded honorary doctorates of laws from the University of British Columbia and the University of Western Ontario.

Simpson has been a member of the board of trustees at Queen's University; the board of overseers at Green College, University of British Columbia; the advisory board of the Review of Constitutional Studies at the University of Alberta; the editorial board of The Queen's Quarterly, and the Canadian Consortium for Asia-Pacific Security at York University and the University of Toronto. He has been vice-chairman of the City of Ottawa Library Board.

Simpson is a Senior Fellow at the University of Ottawa’s Graduate School of Public and International Affairs.[3]

In 2006, Simpson was awarded the Charles Lynch Award in recognition of his outstanding coverage of national issues.

Simpson is also an outspoken critic of the monarchy of Canada and has written in favour of republicanism in his column .

Simpson has authored seven books:

• 1980 - Discipline of Power, winner of the 1980 Governor General's Award for Non-Fiction.
• 1988 - Spoils of Power
• 1993 - Faultines, Struggling for a Canadian Vision
• 1996 - The Anxious Years
• 2000 - Star-Spangled Canadians
• 2001 - The Friendly Dictatorship
• 2007 - Hot Air: Meeting Canada's Climate Change Challenge (co-authored with Mark Jaccard and Nic Rivers)