Guillaume Leahy

Lawyer - Montréal

Québec Bar 2013
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Guillaume Leahy practices civil and commercial litigation in the Montréal office of Langlois Lawyers.

He acts primarily in complex litigation files involving contractual liability, product liability, constitutional law and professional liability issues.

Guillaume advises businesses and organizations active in various industries including mining and metals, technology, port operations, energy as well as construction and defends their interests before civil courts and administrative or arbitral tribunals. He frequently represents foreign clients, particularly in matters involving private international law or international arbitration.

In addition, he has acquired extensive expertise in supervising the work of expert witnesses and managing electronic evidence in litigation matters involving major commercial, strategic and economic issues.

Before joining Langlois Lawyers, Guillaume practiced civil and commercial litigation at a national law firm.


Juris DoctorQueen’s University, Kingston, Ontario, 2013

LL.B, Laval University, Québec, 2011

Rankings & Recognitions

Best Pair of Oralists and 4th Best Appeal Factum at the Laskin Moot, 2013

Agnes Lefas Memorial Scholarship, Queen’s University Faculty of Law, 2013

Honour Roll of Laval University’s Faculty of Law, 2011-2012

First prize at the “Face-to-Face” interuniversity debate competition, 2011

Winner of the Academic prize at the year-end gala of Laval University’s Faculty of Law, 2011

McCarthy Tétrault Leadership Award, Laval University’s Faculty of Law, 2010

Best Appeal Factum at the Pierre-Basile-Mignault civil law moot, 2010

Scholarship for academic excellence, Laval University’s Faculty of Law, 2009

Representative Work

Guillaume’s recent experience includes the following mandates:

International commercial arbitration – Contractual Dispute – Mining Equipment
Represented a multinational industrial equipment manufacturer who prevailed in a $175M ICC arbitration in New York regarding the performance of equipment sold to a mining company and installed at an iron ore concentrator plant.  

Contractual Liability – Oil Company – Motion to Dismiss
Represented a Canadian oil company who prevailed in a motion to dismiss presented to the Quebec Superior Court in a contractual dispute relating to the doctrine of res judicata. 

Contractual Litigation – Share Purchase Agreement – Indemnification Clause
Represented one of Canada’s largest investment fund companies who prevailed in Quebec Superior Court in a contractual dispute over the application of an indemnification clause in a Share Purchase Agreement.

Constitutional Law – Division of Legislative Powers – Navigation and Shipping
Successfully represented a Canadian Port Authority and a bulk liquid transhipment terminal operator in Quebec Superior Court, the Quebec Court of Appeal and the Supreme Court of Canada in a constitutional dispute over the applicability of a provincial environmental protection regime to federal property and to navigation and shipping operations.

Product liability – Industrial, agricultural and construction equipment
Represents manufacturers of industrial, agricultural and construction equipment, as well as contractors, in litigation involving issues regarding the design and performance of various products or works, and the application of legal and contractual warranties.

Telecommunications and Information Technology – Contractual Disputes or Regulatory Compliance
Represents and advises businesses operating in the areas of telecommunications and information technology in contractual disputes, or in connection with the regulatory compliance of their operations.

Professional Liability – Medical Malpractice
Represented physicians and medical clinics in matters involving professional liability, access to information, billing, and disciplinary law.




2014-2020 – Pro Bono Students Canada, Supervising lawyer for the civil law section of the University of Ottawa’s Faculty of Law

2009-2011 – Chairman of the board of directors of Coop Zone (2009-2010) and member of the board of directors (2008 to 2011)

2009-2010 – Harvard National Model United Nations in Boston, Head Delegate, Delegation of the Faculty of Law, Laval University

2009-2010 – Member of the Board of the Student Investment Fund of the Faculty of Law at Laval University

2008-2011 – Member of the Faculty of Law’s Board, Laval University

2006-2007 – Member of the Board of Directors of the Fondation du Cégep de Sainte-Foy

Professional Associations

Since 2013 – Young Bar Association of Montreal

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