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Guillaume Buell

Guillaume Buell focuses on prosecuting complex securities fraud cases on behalf of institutional investors and advises leading pension funds and other institutional investors on issues related to corporate fraud in the U.S. securities markets. He also advises foundations and endowment funds on monitoring the well-being of their investments. Mr. Buell also litigates complex consumer fraud class actions. Mr. Buell is an active member of the National Association of Public Pension Attorneys and the National Association of Shareholder and Consumer Attorneys.

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

  • In re Adient plc Securities LitigationNo. 18-cv-9116 (S.D.N.Y.)
  • Tung v. Dycom Industries, Inc., et al.No. 18-cv-81448 (S.D. Fl.)

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))
  • Wayne County Employees’ Retirement System, et al. v. Mavenir, Inc., et al., Case No. 18-cv-1229-CFC (D. Del.)
  • McComas v. BrightView Holdings Inc., et al., No. 2019-07222 (Montgomery County, Pennsylvania Court of Common Pleas)
  • City of Cambridge Retirement System v. National Mentor Holdings, Inc., No. 12019-0225 (Del. Chancery)

Practice Areas

He has actively assisted in the prosecution of numerous securities class actions across the country, including the following:

  • Medoff v. CVS Caremark Corporation, et al., Case No. 09-cv-554-JNL-PAS (United States District Court, District of Rhode Island) ($48 million settlement reached against the nation’s largest pharmacy retail chain)
  • In re Vocera Communications, Inc. Securities Litigation, Master File No. 3:13-cv-03567 EMC (United States District Court, Northern District of California) ($9 million recovery secured for investors against a leading provider of mobile communication solutions)
  • In re Nu Skin Enterprises, Inc. Securities Litigation, Case No. 2:14-cv-00033-JNP-BCW (United States District Court, District of Utah) ($47 million settlement reached in securities class action involving Nu Skin’s business conduct in China)
  • In re Genworth Financial, Inc. Securities Litigation, Case No. 14-cv-2392 (AKH) (United States District Court, Southern District of New York) ($20 million settlement reached with provider of insurance and wealth management services)
  • In re Castlight Health, Inc. Shareholder Litigation, Lead Case No. CIV533203 (Superior Court of the State of California, County of San Mateo) ($9.5 million settlement with Castlight Inc, in a case alleging that the company’s IPO offering documents were false and misleading because they omitted material information, including significant obstacles and delays faced by customers during the implementation of Castlight’s technology, resulting in low customer renewal rates and negatively impacting the company’s gross margins)
  • Noppen v. Innerworkings, Inc., et al., Case No. 14-cv-1416 (United States District Court, Northern District of Illinois, Eastern Division) ($6.025 million settlement in case alleging misleading statements and omissions regarding accounting improprieties)
  • Hall v. Rent-A-Center, Inc., et al., No. 16-cv-0978 (United States District Court, Eastern District of Texas) (securities class action against Rent-A-Center, Inc., its former CEO Robert D. Davis, and former CFO Guy J. Constant alleging defendants made material misstatements and omissions in violation of the federal securities laws concerning, among other things, the risks and benefits of a new point-of-sale (POS) system that Rent-A-Center began implementing in early 2015)
  • In re Biogen Inc. Securities Litigation, No. 1:15-cv-13189-FDS (United States District Court, District of Massachusetts) (securities class action against Biogen and certain current or former executives relating to misstatements and omissions about its leading MS drug, Tecfidera)

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. Before joining Labaton, he was a litigation associate at Cahill Gordon & Reindel LLP, where he represented major corporations and their officers and directors in the financial, consumer, pharmaceutical, and insurance sectors in commercial and securities litigations and consumer class actions in state and federal courts, state and federal government investigations, and internal investigations. Mr. Buell also honed his trial skills at the boutique litigation trial firm of Hicks Davis Wynn, P.C. in Houston, Texas.

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.

Mr. Buell is active in his local community, serving as a member of the National Eagle Scout Association Committee for the Boston area’s Spirit of Adventure Council of the Boy Scouts of America.

He 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
• U.S. District Court for the District of Massachusetts
• First Circuit Court of Appeals
• U.S. District Court for the Southern District of New York
• U.S. District Court for the Eastern District of New York
• Second Circuit Court of Appeals
• 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