Phone: (617) 531-3933

Practice Areas

Securities Litigation

Guillaume Buell



Guillaume Buell is a Partner of Thornton Law Firm. His practice focuses on representing investors and consumers in securities and consumer lawsuits pending in state and federal courts across the country. Guillaume’s clients include a diverse array of institutional investors and high-net worth individual investors in both the United States and throughout the world. During his lengthy career, Guillaume has also provided legal counsel to a wide range of Fortune 500 and other corporate clients in the aviation, construction, energy, financial, consumer, pharmaceutical, and insurance sectors in state and federal litigations, government investigations, and internal investigations.

Guillaume has been recognized as a "Super Lawyer" for Securities Litigation by Super Lawyers®, a renowned rating service of outstanding lawyers from more than 70 practice areas who have attained a high degree of peer recognition and professional achievement. He had earlier been selected as a "Rising Star" by the same organization.

In addition to his active litigation practice, Guillaume advises leading pension funds, endowments, and institutional investors on issues related to their investments and corporate governance issues. Guillaume is an active member of the National Association of Public Pension Attorneys, the Canadian Pension & Benefits Institute, the Michigan Association of Public Employee Retirement Systems, the National Association of Shareholder and Consumer Attorneys, and the Georgia Association of Public Pension Trustees.

He is admitted to practice in Massachusetts, New York, and Texas, as well as the Supreme Court of the United States, the United States Courts of Appeals for the First, Second, and Ninth Circuits, and numerous federal district courts across the country.

Guillaume is presently litigating a number of important securities and consumer class actions, including cases on behalf of consumers against and class actions on behalf of the shareholders of Adient PLC, Conduent Inc., Cloudera, Inc., Restaurant Brands, and Veeco, Inc.

Prior to joining Thornton Law Firm, Mr. Buell was a senior associate at Labaton Sucharow in New York, where he handled a wide range of securities class actions. Mr. Buell was also previously an attorney with Hicks Davis Wynn, P.C. in Houston and Cahill Gordon & Reindel LLP in New York.

Mr. Buell received his J.D. from Boston College Law School and was the recipient of the Boston College Law School Award for outstanding contributions to the law school community. He was also a member of the National Environmental Law Moot Court Team, which advanced to the national quarterfinals and received best oralists recognition. While in law school, Mr. Buell was a judicial intern with the Honorable Loretta A. Preska, United States District Court for the Southern District of New York. He spent his third year of law school as an intern with the Government Bureau of the Attorney General of Massachusetts. He received his B.A., cum laude with departmental honors, from Brandeis University.

Guillaume is an Eagle Scout and is fluent in French. He is an active member of his local community, including serving in various roles within his church and as a board member of the Boston chapter of the National Eagle Scout Association.

  • Brandeis University, B.A., cum laude, with departmental honors
  • Boston College Law School, J.D., Recipient of Graduate Student Association Law School Award

2021 - Selected as Super Lawyer® by Thomson Reuters’s Massachusetts Super Lawyers® Magazine

2019 - Selected as a Rising Star by Thomson Reuters’s Massachusetts Super Lawyers® Magazine

  • Commonwealth of Massachusetts
  • State of New York
  • State of Texas
  • Supreme Court of the United States
  • First Circuit Court of Appeals
  • Second Circuit Court of Appeals
  • Ninth Circuit Court of Appeals
  • U.S. District Court for the District of Massachusetts
  • U.S. District Court for the Southern District of New York
  • U.S. District Court for the Eastern District of New York
  • U.S. District Court for the Eastern District of Texas
  • U.S. District Court for the Northern District of Texas
  • U.S. District Court for the Southern District of Texas
  • U.S. District Court for the Western District of Texas
  • U.S. District Court for the District of Colorado
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