During twelve years with the Canadian foreign service, MacLaren's postings included Hanoi, Saigon, Prague and the United Nations in New York and Geneva.
His historical book, Canadians on the Nile, 1882–1898 was published in 1978 and the following year he was elected to the House of Commons of Canada as the Liberal MP for Etobicoke North.
In June 1984, he was appointed to John Turner's short-lived cabinet as Minister of National Revenue, but was defeated in the September election by Conservative Bob Pennock.
[1] He also co-Chairs the Canada Europe Roundtable for Business, sits on the Council of the Champlain Society, the Executive Committee of the Trilateral Commission, 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.
While serving as High Commissioner in London, he published the historically significant diaries of explorer William Stairs.