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Mary  Paterson

Mary Paterson

Partner, Litigation

Contact Information

tel: 416.862.4924



Bar Admission

Ontario, 2005

  • Osgoode Hall Law School, LL.B.
  • Osgoode Hall Trial Advocacy Course
  • University of Calgary, B.Comm.
  • University of Calgary, B.A. (English)

Mary was ranked as a Benchmark Litigation Canada 2015 Future Star – Ontario (Class Action; General Commercial). Mary’s commercial litigation practice focuses on tax litigation, class actions, contract disputes in court or in arbitrations and other general commercial litigation, franchise disputes, and assisting stakeholders in receiverships, bankruptcies and proceedings pursuant to the Companies’ Creditors Arrangement Act. Mary has appeared in the Ontario Court of Appeal, the Ontario Superior Court (including the Commercial List), the Federal Court, the Alberta Court of Queen’s Bench, the Manitoba Court of Queen’s Bench, the Supreme Court of Newfoundland and Labrador, and the Tax Court of Canada. Before joining Osler, Mary clerked at the Court of Appeal for Ontario. Mary worked to establish several pro bono programs within the firm and has appeared in the Court of Appeal on a pro bono basis numerous times. She won a 2011 Lexpert Zenith Award for her work assisting a UN employee obtain a widower’s benefit after his same-sex partner died while working for the UN.

  • Benchmark Litigation Canada 2015: Class Action; General Commercial

  • Class Actions

    Class Action Preparedness Brief - Multijurisdictional Matters

    October 26, 2015

  • Walking the Tightrope: How to Manage Risk Today to Prevent Tomorrow's Class Action , Toronto

    October 1, 2015

  • Winner of the 2011 Lexpert Zenith Award for Pro Bono by Associates.
  • Project Work, Board Member
  • Pro Bono Law Ontario, Court of Appeal Amicus Program
  • Pro Bono Law Ontario, Law Help Centre
  • Outside counsel assisting the United Nations Office of Staff Legal Assistance and representing UN employees directly

  • Law Society of Upper Canada
  • The Advocates’ Society (member of Young Advocates’ Standing Committee, 2007-2010)
  • Young Canadian Arbitration Practitioners, Secretary
  • The Osgoode Society

  • Multiple Canadian taxpayers in a dispute with the CRA regarding a tax shelter (trial).
  • Several trustees in disputes with the CRA regarding the residence of the trust, including a trial and appeal.
  • A Canadian company in a dispute with the CRA regarding PAPI.
  • A global remediation company defending breach of contract litigation.
  • An accounting firm in an alleged wrongful dismissal case (trial).
  • The Greater Toronto Airports Authority in action related to the termination of a contract and taxes.
  • A Canadian corporation in a dissenting shareholder dispute (trial).
  • A Canadian bank in a shareholder dispute.
  • An individual in a shareholder dispute.
  • Several Canadian franchisors in franchise disputes.
  • An international company in a patent damages reference (Federal Court).
  • A Canadian company seeking payment from its insurer (Federal Court - trial).
  • Several Canadian Trustees in bankruptcy.
  • Several Canadian court-appointed receivers and monitors.
  • Several international corporations preparing for proceedings in the United States as well as in Canada under the Companies’ Creditors Arrangement Act.
  • A Canadian secured creditor seeking to appoint a receiver.

  • Federal Court Refuses to Certify Tax Class Action, Osler Canadian Class Action Defence Blog, July 29, 2015.
  • First Canadian Decision on Residency of Trusts between Provinces, Osler Update, July 8, 2015.
  • Sattva Capital Corp. v. Creston Moly Corp.: Are Issues of Contractual Interpretation Certifiable in Class Proceedings as Common Issues?, Bank & Finance Law Review, April 2015.
  • Supreme Court Decisions Impacting Franchisors: Contractual Interpretation and Contractual Duty of Honesty, Osler Franchise Review, April 2015.
  • Supreme Court Focuses on Getting to the Merits, Colloque National Sur Les Recours Collectifs – Editions Yvon Blais, March 26, 2015.
  • Procedural Tips for Trial Preparation, OBA Young Lawyers Division: Your First Civil Trial Conference, March 6, 2015.
  • Boilerplate: Tips and Tricks on Drafting, Osler, March 4, 2015.
  • Missed in Translation: Bringing Your U.S. Franchise Agreement to Canada, LJN’s Franchising Business & Law Alert Vol. 21, No. 2, November 2014.
  • Supreme Court of Canada Limits the Right to Appeal Commercial Arbitral Decisions: Contractual Interpretation Is a Question of Mixed Fact and Law, Commercial Litigation and Arbitration Review, November 2014
  • Supreme Court of Canada Limits the Right to Appeal Commercial Arbitral Decisions on Issues of Contractual Interpretation, Osler Update, August 5, 2014.
  • Springdale Pizza: Eleven Decisions on Disclosure, Rescission and Damages (and Counting), Osler Franchise Review, May 2014.
  • Court Rejects Class Action Settlement As Substantively Unfair, Osler’s Canadian Class Action Defence Blog, March 26, 2014.
  • Staying a Third Party Claim: Is the Third Party Bound to Findings in the Common Issues Trial? Osler, Hoskin & Harcourt LLP, March 20, 2014.
  • OBA YLD Conference: Your First Civil Trial – Procedural Tips for Trial Preparation, March 7, 2014.
  • Does Access to Justice Trump Individual Issues? Osler, Hoskin & Harcourt LLP, March 6, 2014.
  • Just Enough: Practical Boundaries of Certification, Colloque National sur les Recours Collectifs, Barreau du Quebec, March 2014.
  • Tips on Drafting Arbitration Clauses, Osler Franchise Review.
  • Limitation Periods Will Continue to Run During the Appeal of a Bankruptcy Order, Weil Bankruptcy Blog.
  • Leave to Appeal Denied – Ontario Court of Appeal Reviews the Test for Leave to Appeal Decisions in CCAA Proceedings, Weil Bankruptcy Blog.
  • Exclusion Clauses Prevent Co-Defendants From Collecting Contribution and Indemnity, Canadian Bar Association National Civil Litigation Section Newsletter, July 2013 (Paul Ivanoff, Mary Paterson and Carly Fidler).
  • Court of Appeal Overturns Pet Valu Decision: Class Members Can Openly Debate Opting Out Without Invalidating Opt-Out Period, Osler Update, May, 2013 (Mary Paterson, Jennifer Dolman and Gillian Scott).
  • Fairness prevails: Ontario Court applies “fraud upon the bankruptcy law” principle to void provision of contract, Weil Bankruptcy Blog.
  • Supreme Court Clarifies “Unlawful Means” Requirement in Tort of Unlawful Interference with Economic Relations, Osler, Hoskin & Harcourt LLP, January 31, 2014 (Mary Paterson and Geoff Hunnisett).
  • The Supreme Court of Canada Seeks to Improve Access to Justice through Expanded Summary Judgment Motions, January 27, 2014 (Mary Paterson, Laura Fric, Catherine Gleason-Mercier).
  • Law Commission of Ontario To Review Class Action Procedure,, January 8, 2014 (Mary Paterson and Christopher Naudie).
  • Arbitration Agreements Can Preclude Competition Claims  and Class Actions, Commercial Litigation, Volume XV, November 2013
  • No way out – Ontario insolvency court approves class action settlement that prohibits any affected person from opting out, Weil Bankruptcy Blog, May 13, 2013 (Mary Paterson and Patrick Riesterer) .
  • Ontario Courts Cannot Validate Foreign Service of Claims Where the Hague Convention Applies, Osler Update, April, 2013 (Mary Paterson and Stephanie Fujarczuk).
  • New York Fries: Court Awards $500,000 Against Franchisees for Defamation, Osler Franchise Review, April 2013 (Mary Paterson and Lia Bruschetta).
  • Federal Court of Appeal Rules that Class Proceedings under the Competition Act Can Be Stayed on the Basis of an Arbitration Clause, Osler Update, March 5, 2013 (Mary Paterson and Christopher Naudie).
  • The Class of 2012: Where Are We Now?, Editions Yvon Blais, March 2013 (Mary Paterson, Sonia Bjorkquist and Karin Sachar).
  • Conflicting Results from Ontario Appellate Courts in Motions to Strike Claims in Proposed Class Actions, Osler Update, February, 2013 (Mary Paterson, Lindsay Rauciio, Karin Sachar and Craig Lockwood).
  • Class Actions in Canada 2012, Osler, Hoskin & Harcourt LLP, January, 2013 (Mary Paterson, Sonia Bjorkquist and Christopher Naudie).
  • Environmental Contamination and Regulatory Orders: Who Pays? Weil Bankruptcy Blog.
  • When can Environmental Regulatory Orders be Compromised Claims under the federal Companies Creditors’ Arrangement Act? Supreme Court of Canada provides clarification, Osler Update, December, 2012 (Mary Paterson, Dan Kirby, Jack Coop, Jennifer Fairfax, Patrick Welsh, Edward Sellers).
  • Multi-Jurisdictional Classes: Does Van Breda Change Anything?, OBA Class Act Vol. 3, No. 1, December 2012 (Mary Paterson and Sonia Bjorkquist).
  • Employers Have a Reasonable Expectation of Privacy in Work Computers - Supreme Court of Canada, Osler Update, October, 2012, (Mary Paterson, Christopher Naudie and Jim Hassell).
  • Litigating a Cross-Border Class Action in Canada, ALM Cross-Border Litigation Forum in New York City, September, 2012 (Mary Paterson, Karin Sachar, Deborah Glendinning and Sonia Bjorkquist).
  • Ontario court of appeal upholds extraordinary DIP financing arrangements in CCAA proceedings over objections of majority creditors, National Insolvency Review, vol. 29 no. 4, August 2012 (Mary Paterson and Edward Sellers).
  • DIP Financing Rules Crystallized: Interim DIP Financing Arrangements Approved by the Ontario Court of Appeal, Weil Bankruptcy Blog.
  • Takin’ Care of Business and Working Overtime: Ontario Court of Appeal Releases Key Decisions on Overtime Class Actions, June, 2012 (Mary Paterson, Laura Fric, Adam Hirsh and Karin Sachar).
  • Supreme Court of Canada Revamps the Test for Jurisdiction Over Foreign Defendants, Osler Update, April, 2012 (Mary Paterson, Andrea Laing, Larry Lowenstein and Robert Carson).
  • Ontario Court of Appeal Holds that Companies Trading Exclusively on Foreign Exchanges Can Be “Responsible Issuers” in Ontario, Osler Update, April 4, 2012 (Mary Paterson, Andrea Laing and Kevin O’Brien).
  • A Cautionary Tale on Privilege Claims by Court-Appointed Receivers, OBA Insolvency News, Volume 28, No. 1, February 2012 (Mary Paterson and John A. MacDonald).
  • Baton Rouge: Juicy Legal Developments on Disclosure Obligations, Osler Franchise Review, March 2012 (Mary Paterson).
  • Multi-Jurisdictional Class Actions: Will the New CBA and ABA Protocols Solve All our Problems?, Développements Récents en Recours Collectifs, Volume 345, Barreau du Québec, March 2012 (Mary Paterson, Mike Eizenga and Sonia Bjorkquist).
  • Court Assigns Dealership Agreement over Ford’s Objections, Toronto Law Journal, January 2013 (Mary Paterson and John MacDonald).
  • Competence-Competence Does Not Apply to Parties Seeking Arbitration, YCAP, 2012 (Mary Paterson).
  • Ontario Court of Appeal Gives Teeth to Summary Judgment Rule, Osler Update, December, 2011 (Mary Paterson, Craig Lockwood, Adam Hirsh).
  • Courts Reject Technical Defences and Allow Rescission, Osler Franchise Review, October 2011 (Mary Paterson).
  • A Lying Bankrupt: A Trustee’s Obligation, Rebuilding Success, Fall/Winter 2011 (Mary Paterson and John MacDonald).
  • What to Do When a Franchisee Summons you to Testify, Osler Franchise Review, May 2011 (Mary Paterson).