He is a Canadian activist. He grew up in Chilliwack, British Columbia, graduating from Chilliwack Senior Secondary School in 1962. He studied at the University of British Columbia and did graduate work at the University of Chicago, obtaining a PhD in the history of religion. After Chicago, he worked for the Canadian Conference of Catholic Bishops for 21 years, serving as Director of Social Policy.
Clarke was the chair of the Action Canada Network, a coalition of labor groups and activists that led the battle against the 1987 Canada-United States Free Trade Agreement. The activists joined forces with anti-free traders from Mexico and the United States to oppose the North American Free Trade Agreement. As a result of his leadership role in the anti-free trade movement, Clarke was fired from the Conference of Bishops. Clarke then wrote Behind the Mitre: The Moral Leadership Crisis in the Canadian Catholic Church (Toronto: HarperCollins, 1995), analyzing the role of the Catholic Church and church-state relations in the previous two decades.
Clarke has continued his activism, working closely with Maude Barlow of the Council of Canadians. In 1997 he formed the Polaris Institute and led the campaigns against the Multilateral Agreement on Investment, the Asia-Pacific Economic Cooperation, and the World Trade Organization.
As a result of his activist work, he and Maude Barlow were awarded the 2005 Right Livelihood Award.
As of December 2011 Clarke sits on the board of directors of the International Forum on Globalization.