John Mather is a partner at DMG Advocates practicing commercial and public litigation.

John is adept on his feet in any setting – his favourite place to be is in court or a hearing room. He regularly appears before the Ontario Superior Court and Court of Appeal. He has acted in numerous domestic and international arbitrations, including in New York and Riyadh, Saudi Arabia. He also represents clients responding to investigations and proceedings before various types of administrative bodies, including the Capital Markets Tribunal (the Ontario Securities Commission) and private sport arbitrations.

John’s commercial litigation work focuses on contractual disputes, product liability, class actions, securities and shareholder claims, commercial real estate and leasing matters, franchise and automobile dealer claims, procurement litigation, and media and defamation. John also acts on urgent matters involving fraud, including successfully obtaining Mareva orders and other extraordinary relief.

John’s public litigation work focuses on public inquiries, regulatory or government investigations and defence of regulatory proceedings. In 2022-2023, John served as Commission Counsel to Justice Rouleau of the Ontario Court of Appeal at the public inquiry investigating the federal government’s invocation of the Emergencies Act in response to the Freedom Convoy protests in January/February 2022. From 2019-2022, John acted as Associate Commission Counsel to then-Associate Chief Justice of Ontario Frank Marrocco at the Collingwood Judicial Inquiry, an extensive public investigation into alleged conflicts of interest and other concerns surrounding two major transactions by the Town of Collingwood.

John has been recognized by Lexpert as a Leading Lawyer to Watch in corporate commercial litigation and has been featured in Benchmark Litigation’s 40 & Under Hot List for 2021 and 2022.

John is a member of the Ontario Bar Association’s Civil Litigation Section executive. He also is a member of the Advocates Society’s Mid-Career Advocates’ Standing Committee (MASC),

Prior to joining DMG Advocates in 2018, John spent five years as an associate lawyer at a leading national firm. John earned his law degree from Western University, where he graduated with Distinction. Prior to law, John worked as a journalist in Canada and the United Arab Emirates.

More information on John’s experience appears below.

Product Liability, Automotive Law and Class Actions

John regularly acts as lead counsel for automobile manufacturers in product liability matters, including complex class actions. John also advises manufacturers on dealer relations and represents them in litigation and arbitration (including under the NADAP Rules).

Beyond the automotive industry, John also represents other designers and manufacturers in defence of a variety of product liability claims.

Public Inquiries, Regulatory Liability, Investigations and Inquests

John is an experienced public inquiry and commission lawyer, serving as both commission counsel and counsel to participants and witnesses. John also represents individuals and organizations that are subject to regulatory investigations and disciplines proceedings, as well as acts as an investigator for companies.
John’s experience on both sides of investigations provide him with a unique perspective into the process, procedure and pressures of investigations, both public and private.

Commercial and International Arbitration

John has appeared as lead counsel in numerous commercial arbitrations, including ad hoc arbitrations and under institutional rules including ICC, UNCITRAL and JAMS. John’s arbitration experience includes urgent hearings for interim measures.

Injunctions and Urgent Proceedings

John has acted in numerous injunctions and urgent proceedings, including proceedings to obtain Mareva orders, evict trespassers and matters involving alleged breaches of confidentiality, non-competition and non-solicitation obligations. As part of this experience, John has successfully prosecuted contempt of court proceedings against parties that fail to comply with court orders.

Commercial Leasing, Construction and Condominium Law

John represents tenants and landlords in commercial leasing litigation and arbitration. John’s clients have included leading restaurant franchisors, real estate developers and office furniture manufacturers. John also regularly advises both condominium corporations and residents on their rights and obligations under Ontario’s Condominium Act.

Procurement Litigation

John has acted in several procurement matters, both public and private. Among other cases, John acted for eHealth Ontario in complex litigation and arbitration relating to the government agency’s decision to terminate a multi-million dollar software development agreement.

Municipal procurement practices were also a focus of the Collingwood Judicial Inquiry, where John served as Associate Commission Counsel. John advises and represents unsuccessful RFP proponents.

Media and Defamation

John regularly acts in defamation proceedings, including pursuing and defending anti-SLAPP motions. As a former journalist, John understands how the risk of litigation can affect reporting, editing and publishing decisions.

Cryptocurrency and Blockchain

John has represented clients in contractual disputes relating to the payment and transfer of cryptocurrency. John advises clients on litigation risk and other aspects of dealing in cryptocurrency and blockchain technologies, including the sale and use of non-fungible tokens (or NFTs).

Cross Border Litigation

John assists US counsel with a variety of cross-border litigation matter. John works cooperatively with US counsel in cross-border class action proceedings. Among other services, John can assist in enforcing foreign judgment and obtaining the evidence of individuals or organizations located in Ontario.

Bar Admission

  • Ontario (2013)


  • Juris Doctor (with Distinction), Western University (2012)
  • Bachelor of Journalism (Honours), Ryerson University (2007)
  • The Advocates’ Society
  • Ontario Bar Association
  • Toronto Lawyers Association
  • Canadian Defence Lawyers
  • Defense Research Institute (DRI)
  • Benchmark Litigation (2021-2023)
    Future Star
  • Benchmark Litigation (2021-2022)
    40 & Under Hot List
  • Canadian Legal Lexpert Directory (2022)
    Leading Lawyers to Watch: Litigation – Corporate Commerial
  • Heywood v. Pleterski (2022): Obtained Mareva order against Aiden Pleterski, the self-described “Crypto King”.
  • Wittal v. Ford Motor Company (2022): Lead counsel on product liability certification motion before Saskatchewan Court of King’s Bench. Decision under reserve.
  • Darvish-Kazem v. Pazkaz Enterprises Inc., 2022 ONSC 1667: Successful defence of an oppression application.
  • Private Settlement (2021): Settled a claim of specific performance for payment of cryptocurrency under a services contract.
  • Private Arbitration (2020): Lead counsel for large restaurant franchisor in rental dispute.
  • Trade Finance Solutions Inc. v. Equinox Global Limited, 2018 ONCA 12, overturning 2016 ONSC 7988: Successful appeal to enforce an arbitration clause.
  • Private Arbitration (2017-2018): Counsel to successful respondent in dispute regarding termination of a mining contract in Saudi Arabia.
  • Private Arbitration (2017): Lead counsel for large restaurant franchisor in a property’s co-owner from evicting a major tenant.
  • 9646035 Canada Ltd. v. Kristine Hill, 2017 ONSC 5252: Successful contempt of court motion.
  • 9646035 Canada Ltd. v. Kristine Hill, 2017 ONSC 5453: Successful trespassing injunction.
  • Campisi v. Ontario, 2017 ONSC 2884: Opposing constitutional challenge to Insurance Act.
  • King v Giardina, 2017 ONSC 1588: Successful motion to stay action for want of jurisdiction.
  • U.S. Steel Canada Inc. (Re), 2016 ONCA 662: Successful defence of appeal confirming that doctrine of equitable subordination does not apply under CCAA.
  • U.S. Steel Canada Inc. (Re), 2016 ONCA 68: Successful defence of an appeal for disclosure of agreement with Industry Canada that was protected by settlement privilege.
  • Speaker: “A Canadian Perspective on Arbitration and Cross Border Litigation”
    The International Network of Boutique Law Firm’s 2023 Chicago Fly-in conference, June 2023
  • Speaker: “Commissions of Inquiry – Lessons Learned for Administrative Tribunals”
    Council of Canadian Administrative Tribunal’s Symposium 2023, June 2023
  • Speaker: “Practical Advice for Bringing and Responding to Applications for Judicial Review” Ontario Bar Association’s Nuts and Bolts of Judicial Review program, April 2023
  • Host: “Considering Exemptions”
    Roundtable at Ontario Bar Association’s 21st Annual OBA Franchise Law Conference, November 2022
  • Chair: “Practical Strategies for Mastering Remote Hearings”
    Program for the Ontario Bar Association, April 2022
  • Speaker: “A Primer on the Canada-European Union Comprehensive Trade Agreement”
    Blakes Business Class, September 2017