Born in Vancouver, British Columbia, Canada, he received a Masters degree from the University of Cambridge, a Master of Divinity and honorary Doctor of Sacred Letter degrees from the University of Toronto, another honorary degree from the University of Alabama, and in 1973 attended Harvard University's Advanced Management Program. In 2002, he received the Alumni Award of Distinction from the University of British Columbia.
His historical book, Canadians on the Nile, 1882-1898 was published in 1978 and the following year he was elected as a Member of Parliament, where he served as the International Trade Minister, responsible for the final stages of NAFTA and the Uruguay Round of GATT, which created the World Trade Organization.
During twelve years with the Canadian Foreign Service, MacLaren's postings included Hanoi, Saigon, Prague and the United Nations in New York and Geneva. From 1996 to 2000, he was High Commissioner for Canada in the United Kingdom and Northern Ireland. He served as the Canadian Chair of the Canada-Europe Round Table, the Canada-India Business Council and the Canadian Institute for International Affairs. He has also served on the Canadian and British Board of Directors of Deutsche Bank AG plus a number of other multi-national corporations. He is also the Honorary Colonel of the 7th Toronto Regiment, Royal Canadian Artillery.
MacLaren sits on the Council of the The Champlain Society, the Board of Directors of the Royal Ontario Museum Foundation Board, is President of St. Catharine's College Society and a director of The Council for Business and the Arts in Canada. His published writings reflect his personal and professional experience, much of it concentrating on Canada's international history.
While serving as High Commissioner in London, he published the historically significant diaries of explorer William Stairs. The depiction on the book cover of the expedition up Mt. Ruwenzori is based on a sketch by William Stairs now in the National Archives.