Phone: (617) 531-3933

Practice Areas

Securities Litigation

Guillaume Buell



Guillaume Buell is a Partner of Thornton Law Firm who focuses his practice on representing institutional and individual investors in securities litigation and arbitrations across the country. Guillaume also advises leading pension funds and institutional investors on issues related to investment and corporate governance issues. He advises leading foundations and endowment funds on monitoring the well-being of their investments. Guillaume is an active member of the National Association of Public Pension Attorneys, the American Association for Justice, the Canadian Pension & Benefits Institute, the Michigan Association of Public Employee Retirement Systems, and the National Association of Shareholder and Consumer Attorneys.

He was named a "Rising Star" for Securities Litigation by Super Lawyers, a rating service of outstanding lawyers from more than 70 practice areas who have attained a high degree of peer recognition and professional achievement. He is admitted to practice before the Supreme Court of the United States, the United States Courts of Appeals for the First, Second, and Ninth Circuits, and numerous district courts across the country.

As chair of the Firm’s securities litigation practice, Guillaume is currently serving as co-Lead Counsel in several federal securities class actions pending across the country, including:

  • In re Adient plc Securities Litigation, No. 18-cv-9116 (S.D.N.Y.)
  • Tung v. Dycom Industries, Inc., et al., No. 18-cv-81448 (S.D. Fl.)
  • Employees Retirement System of the Puerto Rico Electric Power Authority v. Conduent Inc., No. 19-cv-8237 (D.N.J.)
  • In re BrightView Holdings, Inc. Sec. Litig., No. 2019-07222 (Montgomery County, Penn. Court of Common Pleas)
  • Wayne County Employees’ Retirement System, et al. v. Mavenir, Inc., et al., Case No. 18-cv-1229-CFC (D. Del.)

Executive Committee Appointments in Ongoing Litigation:

  • In re Cloudera, Inc., Securities Litigation, Lead Case No. 19CV348674 (California Superior Court, County of Santa Clara)
  • In re Livent Corp. Securities Litigation, Civil Action No. 190501229 (Court of Common Pleas, Philadelphia County)

Furthermore, the Firm and Mr. Buell serve as counsel to plaintiffs in the following actions:

  • Plymouth County Retirement System v. Impinj, Inc., et al., No. 650629/2019 (Supreme Court of New York, County of New York)
  • Iron Workers District Council of New England Pension Fund v. Veeco Instruments, et al., Case No. 18CV332644 (California Superior Court, County of Santa Clara) (consolidated into Wolther v. Maheshwari, et al., Case No. 18CV329690 (Lead Case))
  • Hook v. Casa Systems, Inc., et al., Case No. 654548/2019 (Supreme Court of New York, New York County, Commercial Division)

Before joining the Thornton Law Firm, Mr. Buell was a senior associate with primary responsibility for litigating a portfolio of securities fraud class actions for Labaton Sucharow in New York City. Mr. Buell also has trial and litigation experience from his time with Hicks Davis Wynn, P.C. and Cahill Gordon & Reindel LLP, where he represented clients in the aviation, energy, financial, consumer, pharmaceutical, and insurance sectors in commercial and securities litigations in state and federal courts, state and federal government investigations, and internal investigations.

Mr. Buell received his J.D. from Boston College Law School and was the recipient of the 2009 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.

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