Exceptional solutions. Your needs are as unique as you.

Margaret O’Sullivan

Managing Partner

Location: Toronto, Ontario, Canada
Phone: 416-363-3700
Fax: 416-363-9570


“Margaret O’Sullivan of O’Sullivan Estate Lawyers LLP is highly regarded as a go-to lawyer for cross-border matters, with one source noting: “She is a very technical skilled lawyer and she has got a tremendous amount of experience with multi-jurisdictional estates.”

A market insider remarks: “I think she is an outstanding estate lawyer, without a doubt one of the best in Canada. She has a huge amount of knowledge and technical expertise.

She is fabulous with clients and has great cross-border abilities. She is really one of the leading estate lawyers in Canada.” (Chambers High Net Worth Guide 2022 – Canada, Band 1)

“She is a renowned expert in the field. She completely knows her stuff and has in-depth expertise in this area. She is highly professional, solution-oriented, calm and collected, and very precise. She is very effective in her work, a true professional and her clients are always happy.” Chambers High Net Worth 2019 Canada

The “excellent” Margaret O’Sullivan ranks as one of Canada’s leading private client lawyers. Market sources report that “she is amazing” and that “her name stands out” among peers. Who’s Who Legal Canada, Private Client 2019

“She finds solutions, not problems.” Chambers High Net Worth Guide 2018


Margaret’s practice involves all aspects of trust and estate work for domestic and international private clients, including estate planning; will and trust planning; incapacity planning; estate litigation; advising executors, trustees and beneficiaries and administration of estates and trusts, with a focus on high net worth domestic, cross border and multijurisdictional succession issues.

Margaret is recognized in The Best Lawyers in Canada 2022, Legal Week’s Private Client Global Elite 2022-2023 representing the top 250 private client lawyers worldwide, in the 2022 Edition of The Canadian Legal Lexpert Directory as one of the most frequently recommended estate planning lawyers, both a Global Leader, Private Client 2022 and National Leader, Canada – Private Client 2022.

She is one of nine top-ranked Band 1 private wealth client lawyers in Canada in Chambers High Net Worth 2021 Guide.

Her firm was selected as one of the “Top 10 Wills, Trusts and Estates Boutiques” by Canadian Lawyer Magazine for 2021-22.

She is the recipient of the 2014 Society of Trust and Estate Practitioners (STEP) Founder’s Award for Outstanding Achievement and the Ontario Bar Association’s 2013 Award of Excellence in Trusts and Estates Law.

Prior to establishing an independent practice, Margaret was a partner in the Toronto office of the national Canadian law firm Stikeman Elliott where she directed the firm’s trusts and estates practice.

She has practiced exclusively in the area of trusts and estates since her call to the bar in 1983.

Awards and Accolades

  • Ranked as one of the top 10 Band 1 leading private wealth lawyers in Canada in Chambers High Net Worth 2022 Guide
  • Margaret is recognized as both a Global Leader, Private Client 2022 and National Leader, Canada – Private Client 2022.
  • O’Sullivan Estate Lawyers LLP has been designated a Top 10 Wills, Trusts and Estates Boutique Law Firm for 2021-22 by Canadian Lawyer Magazine
  • Member of Legal Week’s Private Client Global Elite 2022-2023
  • Recognized in the 2022 Edition of The Canadian Legal Lexpert Directory Most Recommended Leading Practitioners in Estate Planning
  • Recognized in The Best Lawyers in Canada 2022 in Trusts and Estates
  • Recognized in the 2021 Edition of The Canadian Legal Lexpert Directory as a Leading Practitioner in Estate & Tax Planning
  • Recognized in The Who’s Who Legal: Private Client 2021
  • Recipient of the 2014 STEP Founder’s Award for Outstanding Achievement
  • Recipient of the Ontario Bar Association’s 2013 Award of Excellence in Trusts and Estates Law

Professional Activities

  • Academician of the International Academy of Estate and Trust Law
  • Member, Private Client Global Elite
  • Elected member, STEP Cross Border Estates Global Steering Committee
  • Fellow, The American College of Trust and Estate Counsel (ACTEC)
  • Member, Canadian Bar Association
  • Member, American Bar Association
  • Member, New York State Bar Association
  • Member, International Bar Association
  • Member, Canadian Tax Foundation
  • Immediate Past Chair for the Queen’s University Gift Planning Advisory Committee
  • Chair of Program Committee for STEP Global Congress, Vancouver, September 13-14, 2018
  • Past Deputy Chair and past member, Board of Directors and Council for STEP Worldwide
  • Past Chair, Professional Standards Committee, STEP Worldwide
  • Founding member and former Deputy Chair, Society of Trust and Estate Practitioners (Canada)
  • Former Chair of the Editorial Board of its newsletter STEP INSIDE
  • Past Chair, Trusts and Estates Section of the Ontario Bar Association
  • Past elected member, Ontario Bar Association Council, 1993-1998
  • Immediate Past Chair of the Queen’s University Gift Planning Advisory Committee



  • The O’Sullivan Team will host an international webinar for members of Mondaq, on “Cross-Border Canada-U.S. Estate Planning and Administration Issues” on Thursday, March 23, 2023.
  • Margaret O’Sullivan will speak on “Estate Planning for the Modern Family,” at the STEP Caribbean Conference, to be held in Panama City, Panama, May 11 – 13, 2023.


  • Margaret O’Sullivan was a speaker on “An Update from Canada” on Canadian developments in estate planning for private clients and family offices at the STEP Cayman Conference – International Wealth Structuring Forum, Grand Cayman, on January 19-20, 2023.
  • Margaret O’Sullivan participated in a panel discussion on a virtual webinar focused on “How are lawyers evolving their estate practices to deliver results?” Topics covered during the webinar included: meeting evolving client needs and innovation beyond people, process and technology. This event was part of the Canadian Legal Innovation Forum Fall Webinar Series on November 8, 2022.
  • Margaret O’Sullivan led a session, organized by the Cambridge Forum, that explored challenging issues around family trusts. The session was be held at Langdon Hall in Cambridge, Ontario, October 23 – 25, 2022.
  • Margaret was on an international panel to discuss the issues and challenges that families regularly face in appointing an executor of a cross-border estate and address the significance of adequate estate planning. Hosted by STEP’s Cross-Border Special Interest Group, on September 27, 2022.
  • Margaret spoke on the topic“The Cross-Border Advisor: Globalization, Populism and Backlash,” at the STEP Global Congress in London, England, July 6 to 8, 2022.
  • Margaret was invited to be both a Member of the Advisory Board and a Presenter at the Private Client Forum Americas, in Mayakoba, Mexico, July 13 to 15, 2022.
  • Margaret with the O’Sullivan Team hosted a webinar for readers of international legal publication Mondaq, on the topic “It’s Complicated: Solutions for Planning and Administering an Estate with Foreign Connections” on March 24, 2022.
  • Margaret was a speaker at “A Conversation with Experienced Estate Planners,” hosted by the Ontario Bar Association (OBA) on January 18, 2022.
  • Margaret spoke on “Cross-Border Estate Planning Considerations, at the “Institute Across Borders: Legal Issues and Best Practices for Ontario Lawyers Around the World,” organized by the Ontario Bar Association (OBA) on November 9, 2021.
  • Margaret presented “Powers of Attorney: The Hurdles Associated With the Practical Use of a Power of Attorney in Today’s World” on the topic of “Cross-Border Recognition of Powers of Attorney” at the Elder Law Online Symposium, organized by the Canadian Bar Association (CBA), on September 24, 2021.
  • Margaret designed and moderated an international webinar, titled “Civil Law and Common Law: A Comparison of Estate Administration on Death,” on Wednesday, June 2, 2021. This event was hosted by the Cross-Border Special Interest Group of the Society of Trust and Estate Practitioners (STEP) Worldwide.
  • Margaret spoke at the International Estate Planning Committee meeting, the American College of Trust and Estate Counsel (ACTEC) Annual Meeting on March 2, 2021, on taxation on death in Canada and inheritance and wealth taxes.
  • Margaret spoke at the Global Elite panel on February 10th, 2021. The panel discussed the pandemic’s impact on the perception of wealth, and shone a spotlight on the topic of a wealth tax (or its lack thereof) across several jurisdictions. Margaret was representing Canada; other panelists were from UK, Italy, Spain, and Switzerland.
  • Margaret and the O’Sullivan team hosted a webinar, “Using Multijurisdictional Wills and Powers of Attorney,” on January 20, 2021, in conjunction with Chambers and Partners. Registrants spanned 43 countries around the world.
  • Margaret spoke on a panel of senior trust and estate practitioners at the OBA Trusts and Estates Section Program on topical issues in estate planning on January 14, 2021.
  • “A Comparative Review of the Use of Will Substitutes.” Margaret moderated this session which included panelists Lionel Smith, law professor at McGill University (expert in common law, estate planning and trusts), and Dr. Gregor Christandl, LL.M. (Yale), associate professor at the University of Innsbruck (expert in civil law and estate planning) on December 1, 2020. The live webcast was part of STEP (Society of Trust and Estate Practitioners) Worldwide Spotlight Sessions.
  • Margaret spoke on the topic of wealth taxes for a presentation by Queen’s University Alumni, on November 24, 2020.
  • “Incapacity at Home and Abroad: Jurisdictional Challenges” – Margaret O’Sullivan was one of three panelists who explored the challenges that can arise from the perspective of both civil-law jurisdictions, such as France, Portugal, and Mexico, and common-law jurisdictions, such as Florida, California, and Arizona, on October 27, 2020.
  • Margaret and the O’Sullivan team of estate lawyers hosted a webinar, “Planning and Administering an Estate with Foreign Connections,” in conjunction with Key Media, publishers of Canadian Lawyer magazine and The Law Times, on September 23, 2020.
  • Margaret attended the American College of Trust and Estate Counsel Annual Meeting in Boca Raton, Florida on March 4-8, 2020.
  • Margaret was a member of the Global Legal Week Private Client Forum Americas Advisory Board that organized the Forum held in Riviera Maya, Mexico on February 5-7, 2020. She spoke on the issue of death taxes and wealth taxes.
  • Margaret helped organize and spoke at the STEP Cross-Border Estates program “Multiple Taxation on Death”, London, U.K. on November 22, 2019.
  • Speaker, OBA Trusts & Estates Section Program on November 11, 2019 on a panel of senior estate planning lawyers to discuss best practices in the area of estate planning.
  • O’Sullivan Estate Lawyers hosted a webinar on the topic “Protecting a Child’s Inheritance,” October 24, 2019.
  • Attended the annual conference of the International Academy of Estate and Trust Law, May 20-23, 2019, Tokyo, Japan.
  • Speaker, “Recent Canadian Estate Planning Developments,” STEP International Tax and Estate Planning Forum: Around the Globe, Laguna Beach, CA May 9 and 10, 2019.
  • Speaker, “Canadian Estate Planning Developments,” Global Legal Week Private Client Forum Americas 2019, Newport Beach, CA March 27-29.
  • Presenter to Faculty Leadership on “Gift Planning on Death,” Queen’s University, Kingston, January 28, 2019.
  • Attended Senior Trust and Estate Practitioners Forum October 14-16, 2018.
  • Presenter, Wills & Estates Planning Seminar, Pal Insurance, October 11, 2018.
  • Chair, Program Committee, STEP Global Congress, Vancouver, September 13-14, 2018.
  • Speaker, Conflict of Laws, STEP Annual Conference, Toronto, May 28-29, 2018.
  • Speaker, Contingency Planning on Death, BloombergSen Women’s event, May 1, 2018.
  • Speaker, Key Estate Planning Issues, Georgian Triangle Lifelong Learning, Collingwood, April 20, 2018.
  • Attended American College of Trust and Estate Counsel Annual Meeting, San Antonio, Texas, March 8 – 11, 2018.
  • Co-chair and presenter, STEP Cross-Border Estates- Mental & Incapacity Session, London, U.K., November 30, 2017.
  • Presenter, Estate Planning Breakfast Workshop, Pal Insurance, November 14, 2017.
  • Attended American College of Trust and Estate Counsel Fall Meeting, Nashville, October 12-22, 2017.
  • Presenter, Cidel Provence Estate Planning Conference, September 2017.
  • Speaker, “Discretionary Trusts – Practical Concerns”, STEP Canada 19th National Conference, Toronto, June 12 -13, 2017.
  • Presenter, Canada-U.S. Cross Border Estate Planning Issues, National Bank, Toronto, June 7, 2017.
  • Speaker, “Estate Planning for Global Families”, STEP Toronto, April 12, 2017.
  • Speaker, Technologic: Technological Liberation and the Transparency of Trust”, Mayan Riviera, Mexico, February 15-17, 2017.
  • Presenter, Gluskin Sheff + Associates Inc., Private Client Lunch Seminar, February 9, 2017.
  • 2016 CBA Wills, Estates and Trusts Fundamentals for Estate Practitioners program, “Conflicts of Laws”, Toronto, October 26, 2016.
  • Canadian Tax Foundation, 2016 Ontario Tax Conference, Co-Presenter: “Multijurisdictional Estate Planning”, Toronto, October 25, 2016.
  • Law Society of Ontario Practice Gems: The Administration of Estates program, Presenter: “Issues Arising Where There Are Foreign Beneficiaries or Legal Representatives of an Estate”, Toronto, September 20, 2016.
  • 2016 STEP National Conference, Panel Presentation: “The Impact of the European Regulation on Succession in Canada”, Toronto, June 10, 2016.
  • CBA Wills, Estates and Trusts Fundamentals for Estate Practitioners program, “Conflict of Laws,” Toronto, October 15-18, 2015.
  • 2015 Cidel Provence Conference, “Multijurisdictional Incapacity and Will Planning for the Mobile Client,” Provence, France. September 2015.
  • OBA Litigation and Administration of Foreign Trusts and Assets program, “Critical Guidance for the Planning and Administration of Foreign Assets,” Toronto, April 9, 2015.
  • Estate Planning & Litigation Forum, “Losing Your Marbles at Home and Abroad: Mental Incapacity and Multijurisdictional Planning,” Langdon Hall, Cambridge, Ontario, April 28, 2015.
  • STEP Journal, Book Review of John Poyser’s Capacity and Undue Influence, March 2015.
  • Private Client Forum Americas 2015, “War Within: Mental Incapacity and Cross-Border Planning for Assets in Multiple Jurisdictions” (Panel Discussion), Papagayo Bay, Costa Rica, February 4-6, 2015.
  • Knowledge Bureau Workshop, “Attorney School: Handling Financial Affairs for a Loved One,” Toronto, November 29, 2014.
  • STEP Global Congress 2014, “Multijurisdictional assets — challenges for estate planning and dealing with mental incapacity,” Miami, Florida, November 6 & 7, 2014.












  • Margaret has been an expert columnist for Advisor.ca and Advisor’s Edge magazine since 2011.
    You may read her columns here.