Mark’s practice focuses on resolving tax and tax-related public law disputes. He represents many of Canada's and the world's largest and most sophisticated businesses in a wide range of tax matters. He has particular expertise in proactively analyzing and advising on tax litigation risks, navigating sensitive tax audits, negotiating with federal and provincial tax authorities, and litigating tax assessments and CRA administrative actions. Described by clients as "the consummate professional" in Chambers and Partners' 2020 Guide to Canada's Leading Lawyers for Business, Mark develops and executes comprehensive and practical strategies for resolving tax disputes as efficiently and favourably as possible, both in and out of the courtroom.
An exceptional litigator, Mark has successfully represented many clients in administrative appeals and before federal and provincial courts, including the Tax Court of Canada, the Federal Court, the Federal Court of Appeal, the Ontario Superior Court of Justice, the Court of Appeal for Ontario, the Court of Appeal of Alberta, and in resisting leave to appeal before the Supreme Court of Canada. The Federal Court of Appeal observed as follows in a 2013 judicial review application: "In exemplary fashion, Mr. Tonkovich untangled a confusing body of evidence and argument, discerned the most important legal issues, and effectively presented submissions that were of significant assistance to the Court in the efficient resolution of this case."
Before joining Blakes, Mark was a tax partner at a prominent international law firm. Prior to that, he was a government tax litigator with the Department of Justice and a judicial clerk at the Federal Court of Appeal.