Before joining Torys, John worked as a constitutional lawyer with the Ontario government and senior policy adviser with the Ontario Cabinet Office. He also spent two years teaching international trade law, international commercial arbitration and international human rights law at Otago University in New Zealand. Further, he served as a clerk to Mr. Justice Cory of the Supreme Court of Canada, and to the judges of the Ontario Court of Appeal.

John teaches International Commercial and Investor-State Arbitration and Public International Law at the University of Toronto Faculty of Law as an Adjunct Professor, and teaches advocacy with the Foundation for International Arbitration advocacy in Geneva. He has also taught public law in the Bar Admission Course and participates as a judge and faculty member for trial advocacy courses and various competitive moots, including the Niagara International Moot and Vis Moot in Vienna.

He is the co-author of three books: Creditors' Remedies in Ontario; Interlocutory Proceedings: Strategy and Practice; and The Emotional Consequences of Personal Injury: A Handbook for Psychiatrists and Lawyers. He has also written numerous other articles and delivered speeches, primarily on international law and constitutional issues.

John is the director for the Canada-EU Mining Council and for Outward Bound Canada. He is also a founding member of Canadian Lawyers for International Human Rights and he sits on the advisory board for the Canada-United States Law Institute of the University of Western Ontario. In addition, he is a member of the International Chamber of Commerce (ICC) arbitration roster for Canada.