Skip to main content

Sean T. Prosser


[email protected]



Sean is a highly experienced litigator with significant experience defending clients facing shareholder litigation, SEC, FINRA, and DOJ investigations and enforcement actions, and other civil and criminal government and regulator investigations and enforcement proceedings. His clients have included public and private companies, officers and directors, board committees, broker-dealers, banks, investment advisors, hedge funds, certified public accountants, individual stock traders, and public officials.

A former SEC enforcement attorney, Sean has defended many clients in securities investigations and white-collar actions initiated by regulatory authorities across the country and with a focus on California, including the US Securities and Exchange Commission (SEC); US Department of Justice, including Department of Treasury; FINRA; NYSE, NASDAQ, and other stock exchanges; California Department of Business Oversight; and the Public Company Accounting Oversight Board (PCAOB).

Through his substantial securities litigation practice, Sean regularly defends public companies and their executives facing shareholder lawsuits and derivative actions in state and federal courts across the country, including in the Delaware Court of Chancery.

Prior to joining Mintz, Sean led the Southern California white collar, government investigations, and securities litigation practices of a leading international law firm. He was also a partner with another international practice as well as with a leading global intellectual property law firm.
Sean started his career as an attorney in the SEC’s Office of Enforcement and as a law clerk in the SEC’s Office of Broker-Dealer Enforcement.

He is frequently quoted in national legal and business publications on various topics, including SEC investigations and related legal matters.


Class Action, Derivative & Corporate Control Litigation

  • Representing RYVYL Inc. and its current and former directors and officers in a shareholder class action and two related shareholder derivative lawsuits pending in the Southern District of California.
  • Negotiated a rare voluntary dismissal of a shareholder class action in the Central District of California against Fulgent Genetics, Inc. after lead plaintiff appointment and without any payment by our client.
  • Represented the former CFO of Fat Brands, Inc. in a shareholder class action in the Central District of California, which was settled without any payment by our client.
  • Obtained judgment following a successful motion to dismiss on behalf of an investment entity and its owner in a federal lawsuit filed by a microcap public company related to convertible notes and warrants (S.D. Cal. July 28, 2022).
  • Secured a complete motion to dismiss victory in a securities class action case on behalf of a large multinational operator of membership warehouse clubs, and its former executives. The case, brought in the Southern District of California, centered on allegations that the company misled the public about its performance, among other missteps.
  • Obtained voluntary dismissal of public company officer and director sued by business partner in California state court.
  • Represented JMP Group, a highly regarded capital markets firm, and its directors in ten shareholder lawsuits filed in federal courts across the country based on claims arising from the acquisition of JMP Group by Citizens Financial Group.
  • Represented Blackhawk Gold, LLC and its related entities in an EB-5 investor class action and related SEC enforcement issues. Negotiated class settlement in which our client agreed to take a specific corporate governance action but without the payment of any money (District of Idaho).
  • Represented Quartzburg Gold, LLC and its related entities in three EB-5 investor lawsuits involving claims of securities fraud. Negotiated full voluntary dismissal of all cases without prejudice and without payment of any money by our clients (W.D. Washington).
  • Represented multiple public companies in connection with shareholder books and records inspection demands and related litigation under 8 Del. Code § 220 and California law.
  • Represented a worldwide provider of global IT and enterprise application solutions and its officers and directors in a federal shareholder class action in the Central District of California and in shareholder derivative litigation in California and Nevada state courts. The matters settled on favorable terms.
  • Represented a leading investment company in a pension plan lawsuit filed in the Central District of California. The plaintiff voluntarily dismissed the complaint.
  • Represented former officers and directors of a restaurant chain operator in connection with breach of fiduciary duty claims by the bankruptcy trustee. Negotiated a resolution without any payment by our clients.
  • Represented a global specialty pharmaceutical company in a shareholder class action lawsuit arising from its $1.3 billion acquisition of another pharmaceutical company.
  • Represented a manufacturer of specialty chemicals and its directors in shareholder class action lawsuits filed in Nevada State Court and Delaware Chancery Court arising from a $400 million tender offer by investment funds.
  • Represented a multinational holding conglomerate and its subsidiaries in shareholder class action lawsuits filed in Kansas state and federal courts arising from the company’s $22 billion acquisition of a large U.S. telecommunications company. Successfully won a stay of a parallel federal court proceeding.
  • Represented a multinational holding conglomerate and its subsidiary in a shareholder lawsuit arising from a large U.S. telecommunications company’s $4 billion acquisition of another telecommunications provider.
  • Represented a provider of surgical aesthetics products and its directors in shareholder class actions arising from a $1.1 billion acquisition by a multinational medical device, pharmaceutical, and consumer-packaged goods manufacturing company. Successfully obtained orders denying a motion for preliminary injunction in a California action and staying a parallel Minnesota action. Won summary judgment in the clients’ favor following discovery. Affirmed on appeal.
  • Represented a leading provider of fingerprint identification systems and its directors in shareholder class action lawsuits filed in California state and federal courts and in Delaware Chancery Court arising from the company’s $943 million acquisition by a leading R&D company making a wide range of products. Successfully defeated the plaintiffs’ motion to enjoin the transaction, negotiated voluntary dismissal of the federal lawsuit, and obtained a stay of the parallel California lawsuit. Negotiated a favorable settlement.
  • Represented a company providing fundraising software and its directors and officers in a shareholder derivative lawsuit in San Diego County Superior Court. Following a successful motion to stay discovery and demurrers on behalf of the company and the individuals, the plaintiff dismissed the case.
  • Represented a multinational IT equipment provider and its officers and directors in a federal class action (Central District of California) and state shareholder derivative (Orange County, California) litigation. Favorably settled all litigation following successful federal motions to dismiss.
  • Represented a San Diego–based defense solutions provider and its officers and directors in multiple federal class actions (Southern District of California) and federal and state court shareholder derivative actions (Southern District of California/San Diego Superior Court). Following successful motions, negotiated a favorable global settlement of all matters, including resolution of complex insurance issues.
  • Represented two former officers of a multinational gaming company in connection with a federal class action (District of Nevada) and Nevada state and federal derivative actions. Dismissal affirmed on appeal.
  • Represented the former CEO of a diagnostics solutions company in California state court shareholder litigation. Settled with no payment by the client.
  • Obtained judgment after trial in favor of client in a control lawsuit involving a closely held company in Delaware Chancery Court before Vice Chancellor Parsons.

White Collar & Regulator Enforcement Investigations and Proceedings

  • Secured rare motion to dismiss victory against the SEC on behalf of Kingston Diversified Holdings, LLC, an investment entity, in an enforcement lawsuit filed in the District of Nevada (September 7, 2022).
  • Representing $1.5 billion public company in SEC investigation related to financial statements.
  • Representing an investment advisory firm and its owners in an SEC enforcement lawsuit in S.D. Cal. alleging various fraud-based claims.
  • Representing federal court mandated Independent Manager of EB-5 Funds and related companies arising from SEC enforcement action (D. Idaho).
  • Representing oil exploration company in pending SEC investigation related to financing activities.
  • Represented U.S.-based traders in highly publicized SEC lawsuit and a DOJ investigation arising from a foreign hack of the SEC’s EDGAR database. Settled SEC action for a fraction of alleged gains and DOJ declined to prosecute our clients (District of New Jersey).
  • Represented a $1+ billion foreign company and a principal shareholder in a DOJ investigation, grand jury, and asset-blocking action by the Office of Foreign Assets Control (OFAC). Successfully obtained the return of over $30 million from OFAC.
  • Represented mineral exploration company in SEC investigation related to business partner’s financial statement disclosures. No action taken against our client.
  • Represented corporate attorney for public company involved in SEC investigation related to alleged market manipulation. No action taken against our client.
  • Represented investment company in investigation by SEC’s Division of Asset Management related to portfolio valuation and management fee issues.
  • Represented foreign defendants in an SEC insider-trading action arising from alleged misappropriation of an investment bank’s information. (Southern District of New York)
  • Represented a law firm and its partners in potential adverse proceedings by SEC receiver appointed in connection with large Ponzi scheme. Secured reasonable settlement wholly paid by insurance as well as a bar order preventing investors and others from pursuing claims against our clients.
  • Represented the Corporate Monitor of a large multinational medical device company arising from joint SEC and DOJ actions under the US Foreign Corrupt Practices Act (FCPA).
  • Represented multiple companies and executives in U.S. Attorney investigations and Grand Jury proceedings.
  • Represented multiple securities traders in SEC insider-trading investigations.
  • Represented an individual regarding an investigation by the SEC’s Los Angeles office into capital raising by an electronics company.
  • Represented securities traders in an investigation by the SEC’s Chicago office related to alleged market manipulation activities.
  • Represented an NYSE-listed company in an investigation by the Financial Industry Regulatory Authority (FINRA) regarding disclosure and securities trading activities.
  • Represented investment advisors and brokers in multiple FINRA investigations.
  • Represented a major apparel company in an investigation by the SEC’s Los Angeles office related to securities disclosure issues.
  • Represented the CFO of a technology company in an investigation by the SEC’s Home Office regarding selective disclosure issues.
  • Represented a medical device company in an SEC investigation related to disclosures involving a then-pending FDA application for approval of medical devices. The investigation closed with no enforcement recommendation.
  • Represented a former general counsel of a public biotechnology company in connection with a joint SEC and DOJ investigation into Foreign Corrupt Practices Act (FCPA) issues involving China.
  • Represented a former general manager of a Chinese company in connection with an SEC investigation into FCPA issues involving a U.S. public company.
  • Represented the chief scientist of a public life sciences company in connection with SEC and DOJ investigations regarding test data. The investigations closed with no enforcement recommendations as to the client.
  • Represented an entertainment company in an SEC investigation regarding film financing.
  • Represented a public accounting firm and CPAs in multiple SEC investigations conducted by Denver, New York, Washington, DC, Chicago, and Miami offices.
  • Represented a securities trading software and education company in an SEC investigation.
  • Represented a broker-dealer in an SEC investigation regarding cherry-picking activities by hedge fund customers. No enforcement action was taken against the client.
  • Represented a broker-dealer and an investment advisor in connection with federal grand jury and other government proceedings relating to potential money laundering issues.
  • Represented a broker-dealer in a FINRA investigation regarding registered foreign agents and anti-money laundering issues.
  • Represented a secretary of a former senior US House of Representatives member in connection with grand jury proceedings.
  • Represented a former officer of a public gaming company in an SEC enforcement action and litigation alleging insider trading based on non-public material information concerning the company’s financial performance.
  • Represented a major publishing company in connection with an investigation by the SEC’s Pacific Regional Office arising from a $250 million accounting restatement.
  • Represented a San Diego City Council member and former acting mayor in an SEC investigation related to municipal bond offering disclosures.

Internal Investigations

  • Represented the audit committee of a major consumer goods company regarding an internal investigation in response to a whistleblower complaint.
  • Represented chairman of the board of a multibillion-dollar medical diagnostic company in connection with an audit committee internal investigation and a NASDAQ investigation regarding disclosure issues.
  • Represented a special committee of a public biotechnology company regarding an internal investigation in response to a shareholder demand regarding stock option plan issues.
  • Represented the chief executive officer of a public technology company in connection with an internal audit committee investigation.
  • Represented the audit committee of a $1 billion public communications company in connection with an internal investigation and an SEC inquiry arising from an accounting restatement.
  • Represented the special committee of a public technology company in connection with an internal investigation and an SEC inquiry regarding stock option backdating issues.
  • Represented multiple public companies in internal investigations and responses to stockholder demands regarding stock option plans.
  • Represented multiple public companies in connection with internal investigations stemming from purported whistleblower complaints.
  • Represented multiple individual officers, directors, and employees of public companies in connection with internal investigations.
Read less


In 2021, approximately on quarter of all federal securities fraud class action lawsuits filed nationwide were against life sciences companies and their officers and directors. These considerations are for directors and officers of life sciences companies looking to manage disclosures and mitigate risk before a suit ever gets filed.
Read more

Federal Jury Concludes Cryptocurrency Products NOT Securities

November 4, 2021 | Blog | By Sean T. Prosser, Edmund P. Daley

A Connecticut federal jury just answered one of the biggest questions on the minds of cryptocurrency investors, developers, and regulators – are cryptocurrencies securities? The jury concluded that Paycoin and several cryptocurrency mining-related assets are not securities.
Read more

SPAC Chat Ep. 4: Litigation Update: Preparing for the Next Wave of Suits Against SPACs

April 27, 2021 | Podcast | By Jeffrey Schultz, Sahir Surmeli

It seems that everyone is taking a second look at SPACs as the number of lawsuits against these alternative IPOs continues to increase by the day.
Read more
Read less

News & Press

Press Release Thumbnail
Mintz is pleased to announce that 120 firm attorneys have been recognized as leaders by Best Lawyers® in the 2024 edition of The Best Lawyers in America©.
Press Release Thumbnail
BOSTON – Mintz has earned top rankings in the 2023 edition of Legal 500 United States guide. The firm is recognized in 14 practice categories, and 59 individual attorneys are also recognized in the guide, some in more than one category.
News Thumbnail
In an article published by the Wall Street Journal, Mintz Member Sean Prosser was quoted on behalf of his client, Sung Cho, a defendant in a U.S. Securities and Exchange Commission (SEC) enforcement case accused of participating in an international trading ring that used stolen corporate earnings releases.
News Thumbnail
Sean Prosser, a former U.S. Securities and Exchange Commission enforcement attorney, joined Mintz as a member of the litigation department to represent clients facing shareholder litigation and SEC and U.S. Department of Justice investigations and enforcement actions.
Sean Prosser was the leader of Perkins Coie's white-collar, government investigations and securities litigation practices in Southern California before he joined Mintz.
Read less

Events & Speaking


Whistleblower Update - The Impact on Corporations and SEC Enforcement

Securities Enforcement Forum West 2022

Palo Alto, California

Conference Reference Image

Cryptocurrency Regulation, Enforcement and Litigation

Securities Enforcement Forum West


Webinar Reference Image

The Securities and Exchange Commission

SEC 32nd Annual Joint Regulatory Conference

Sheraton Grand Los Angeles Hotel 711 South Hope Street, Los Angeles, CA 90017


Corporate Directors Forum

Essentials of Corporate Directorship: Preparing for Your First Board Seat

3580 Carmel Mountain Rd #300 San Diego, CA 92130


Securities Enforcement Forum West 2019

Fours Seasons Hotel Silicon Valley East Palo Alto, California

Read less

Recognition & Awards

  • Best Lawyers in America: Commercial Litigation (2010-2024), Corporate Compliance Law, Corporate Governance Law, Litigation - Securities (2011-2024),  Criminal Defense: White Collar (2023-2024)
  • San Diego Super Lawyers: Securities Litigation (2020)
Read less