Mark Tonkovich
Partner | Toronto
Toronto: 416-863-5258

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.

  • Trial-level tax disputes concerning the general anti-avoidance rule (GAAR), the taxation of foreign affiliates, transfer pricing adjustments, foreign entity characterization, the scientific research and experimental development (SR&ED) program, and the tax consequences of employee fraud

  • Appellate-level cases concerning the GAAR, business vs. property income issues, employer-provided taxable benefits, and the implementation of the provincial reassessment waiver regime

  • Appellate-level judicial intervention on behalf of the Canadian Bar Association concerning fundamental precepts of solicitor-client privilege in the tax context

  • Applications for judicial review concerning failures by the Canada Revenue Agency (CRA) to issue timely assessments of federal income tax, compelling the refund of erroneously-remitted Part XIII withholding tax, disputing the validity of CRA audit requirements, challenging the CRA's refusal to provide relief from double taxation under the Canada-US Tax Treaty, and navigating the intersection of employment insurance and bankruptcy law

  • Provincial rectification proceedings to correct substantial transactional errors in a cross-border hybrid refinancing plan

  • Administrative appeals relating to foreign accrual property income, non-resident withholding tax, payments in respect of intellectual property, the thin capitalization rules, errors in the presentation of financial information, income vs. capital characterization issues, federal sales tax and the financial service exemption, provincial sales tax on insurance products, and the scope and validity of provincial income tax assessments

  • Submissions to the CRA's Transfer Pricing Review Committee overcoming the proposed application of transfer pricing penalties

  • Both frontline and behind-the-scenes guidance on a large number and variety of complex tax audits, including in the context of reviews by the CRA's Aggressive Tax Planning Division, the foreign affiliate regime, transfer pricing issues, entitlement to benefits under Canada's tax treaties, the reporting of offshore assets, employee/independent contractor classification and the SR&ED program

  • Voluntary disclosure submissions concerning a complex web of cross-border transactions involving dozens of legal entities, offshore asset reporting issues, and substantial errors under various provincial sales tax regimes

  • Providing post-transaction opinions on specific tax risks, focusing on the viability of client tax positions and the proactive management of litigation risks and other sensitive matters


Mark is recognized as a leading tax lawyer in the following publications:

  • World Tax/International Tax Review’s Tax Controversy Leaders 2020 – Highly Regarded

  • Chambers Canada: Canada’s Leading Lawyers for Business 2020 (Tax Litigation)

  • The Best Lawyers in Canada 2020 (Tax Law)

  • World Tax/International Tax Review’s Tax Controversy Leaders 2019 – Highly Regarded

  • The Best Lawyers in Canada 2019 (Tax Law)

  • International Tax Review's Tax Controversy Leaders Canada 2018

  • International Tax Review's Tax Controversy Leaders Canada 2017

Show Past:
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Co-author: Striking a Balance: Exploring Legitimate Expectation and the Fisc's Administrative Positions in Canada, the UK, and the US
Tax Litigation, Vol. 22, Issue 2, p. 2, Federated Press, 2019.
Co-author: Future Law and Alternative Facts in the GAAR Analysis
Tax Litigation, Vol. 21, Issue 1, p. 6, Federated Press, 2018.
Co-author: After IGGillis Holdings: Protecting privilege when giving common legal advice
CBA National, March 26, 2018.
Co-author: FCA Rules CRA Cannot Force Taxpayers to Self-Audit on Uncertain Tax Positions
Taxation Law Section Newsletter, Ontario Bar Association, May 15, 2017.
Author: Theft by Owners or Senior Employees: Deductibility of Losses
Canadian Tax Focus, Vol. 6, Issue 1, pp. 1-2, 2016.
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Co-presenter: Transfer Pricing – Law and Practice
International Fiscal Association YIN Seminar, IFA Canada, March 2019.
Co-presenter: Current Cases Seminar
Ontario Tax Conference, Canadian Tax Foundation, October 2018.
Mentor: Speed Mentoring – Practical Advice on Succeeding as a Young Tax Lawyer
Taxation Law Section Seminar, Ontario Bar Association, October 2018.
Panellist: Best Practices to Deal with Canadian Tax Authorities and Audits
Canadian Tax Workshop for US Companies, Council on State Taxation, September 2017.
Panellist: Need to File an Appeal – Procedures to Object and Appeal Canadian/Provincial Tax Assessments and Customs/Duties (Including Input GST)
Canadian Tax Workshop for US Companies, Council on State Taxation, September 2017.
Chair: Year-End Address
Taxation Law Section Year-End Seminar, Ontario Bar Association, June 2017.
Speaker: Tax Challenges in Taking Your Business International
Trade Accelerator Program, Toronto Region Board of Trade, March 2017.
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Quoted: Federal Court of Appeal gives guidance to CPP filing obligations of retired business partners
Interviewed by Terry Davidson, The Lawyer’s Daily, June 18, 2018.
Quoted: Federal Court of Appeal clarifies reach of solicitor-client privilege
Interviewed by Amanda Jerome, The Lawyer's Daily, March 14, 2018.
Quoted: The CBA’s intervention on common interest privilege
Interviewed by Yves Faguy, CBA National Magazine, October 5, 2017.
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