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  1. Professionals

George Mastoris

Partner

Co-Chair, New York Litigation Practice

New York

+1 212-294-4623

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  • Overview
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An accomplished litigator, George represents a broad array of companies involved in high-stakes and high-profile civil and criminal litigations, arbitrations and appeals. He co-heads the New York Litigation Practice and his experience spans a number of substantive areas, including antitrust, securities, insurance, financial technology, and bankruptcy. George’s clients include some of the world’s largest financial services companies, insurance companies and multinational manufacturing concerns, as well as blockchain and biotechnology startups, retailers, and private equity firms.

George has served as lead counsel in price-fixing, cartel and monopolization cases; class actions; trade secret and restrictive covenant cases; government investigations and enforcement actions; RICO actions, and complex commercial litigation. He works closely with his clients to assess and understand both their business and legal interests, and the strategic and tactical advice he provides is squarely and relentlessly focused on pursuing those goals. As a result, his clients, which include some of the most successful and innovative companies in the world, regularly turn to him and his teams for assistance with some of their thorniest legal issues. George represents both plaintiffs and defendants in litigations, adversary proceedings, and appeals, and has argued on their behalf in state and federal trial and appellate courts throughout the country. He has a deep wealth of experience in all phases of litigation, including the early and honest evaluation of claims and defenses, the briefing and argument of dispositive motions, and the development of an efficient, focused, and flexible strategic plan for winning on summary judgment or at trial (or forcing a favorable settlement) rather than simply “managing a process.”

George also counsels clients in connection with regulatory and compliance issues relating to antitrust, securities, and financial technology, including digital assets and cryptocurrency, and has been recognized nationally for his work in the latter two areas. He is also extensively involved in pro bono work at the trial and appellate level, and is especially proud of the results he and his clients have been able to achieve in the areas of voting rights and ballot access.

Key Matters

  • City of Philadelphia, et al. v. Bank of America, et al. Counsel for Goldman Sachs & Co. in multi-billion dollar antitrust matter alleging that competitor banks conspired to fix interest rates for municipal bonds
  • Sizemore et. al. v. Zhao et al. As lead counsel for Defendant Binance US, obtained complete dismissal for in massive class action alleging securities laws violations arising from sale and promotion of digital assets
  • Licht v. Binance Holdings Ltd. et al. and Gonzalez v. Binance Holdings Ltd. et al. Lead counsel for Defendant Binance US in two civil RICO actions alleging involvement in so-called “pig butchering” schemes
  • Sjunde AP-Fonde v. Goldman Sachs & Co. LLC et al. Counsel for Goldman Sachs in high-profile Rule 10(b)(5) securities class action litigation
  • RIA R Squared v. DW Partners et al. Lead counsel in fraud and breach of contract action arising from three large commercial real estate transactions; successfully appealed dismissal of case brought by prior counsel
  • Azad v. Jenner. Represent Caitlyn Jenner and her manager in federal securities fraud and state law class action arising from sale and marketing of digital assets
  • In re Interest Rate Swaps Antitrust Litig. and Iowa Public Employees Retirement Assoc.et al. v. Bank of America Corp., et al. Counsel for defendant Goldman Sachs & Co. in two multi-billion-dollar antitrust putative class actions; obtained complete denial of class certification in Interest Rate Swaps matter
  • FM Global. COVID-19 litigations. Counsel for one of the world’s largest property and casualty insurers in over 12 litigations involving billions of dollars in claims for damages stemming from COVID-19 pandemic
  • Represent defendant in Title VII class action alleging religious discrimination arising from COVID-19 vaccination policy. Secured significant victories in several of those matters to date. 
  • MH Sub I et al. v. Muehter. Successfully enjoined defendant executive from joining competitor company for the entire term of his non-compete provision in restrictive covenant and misappropriation action
  • In re DBMP LLC; In re Aldrich Pump LLC, et al. Counsel for asbestos claimants creditors in proceedings arising out of separation of billions of dollars of asbestos liabilities from solvent companies’ assets
  • NYU Medical Center v. Factory Mutual Insurance Co. Argued and won summary judgment in US$1.6B claim arising out of damage caused by Superstorm Sandy; decision recently affirmed by the Second Circuit
  • Harmoni International Spice Corp. v. Bai, et al. Lead day-to-day counsel for plaintiff in high-stakes antitrust and civil RICO action against a cartel of foreign agricultural producers and their affiliates in the United States; argued and won Ninth Circuit appeal of district court dismissal
  • FCPA Investigation and Related Litigation. Represented major financial institution in multi-billion-dollar DOJ investigation along with follow-on derivative and class action securities litigation
  • In the Matter of Gladius Network LLC. Lead counsel for cybersecurity company in government investigation relating to digital assets; negotiated groundbreaking no-penalty settlement with SEC
  • In re Caesars Entertainment Operating Co. Counsel to Examiner in a massively complex investigation of 27 separate debt and real estate transactions involving billions of dollars
  • Financial Technology Investigations and Advice. Regularly advises financial technology companies in connection with compliance issues and regulatory proceedings involving digital assets and securities law
  • In re ODD Antitrust Litigation. Represented Panasonic Corp. in billion dollar antitrust class action alleging price fixing of optical disc drives. Helped lead joint defense group’s successful efforts to defeat motion for class certification, including briefing motions and overseeing expert phase of case
  • Omnicare v. United Healthcare, et al. Counsel in US$1.4B price-fixing and fraud action arising out of the merger between health care conglomerates United Healthcare and PacifiCare
  • Sheridan Healthcorp, Inc. v. Avmed, Inc. Obtained extremely favorable settlement for group of plaintiff anesthesiologists in federal and state monopolization actions against Florida HMO
  • Voting Rights Cases. Represented Common Cause NY, ACLU, and NYCLU in successful negotiations with New York State Board of Elections and Governor’s office regarding ballot access issues
  • Aguilar v. Immigration and Customs Enforcement. Trial counsel to group of families subjected to pre-dawn raids by ICE; helped obtain US$1M settlement and injunctive relief

George was selected to Lawdragon’s “500 Leading Global Cyber Lawyers” in the area of Litigation, inc. Digital Assets, Cryptocurrency in 2024 and 2025, and “500 Leading Global Antitrust & Competition Lawyers” in 2025. He was recognized as a “Key Lawyer” in the 2024 edition of The Legal 500 US in the area of Dispute Resolution: Securities Litigation: Defense. He was named a “2019 Technology Law Trailblazer” by the National Law Journal, which recognized him for his groundbreaking work in connection with securities regulation and digital assets, and as a “Rising Star” by New York Metro Super Lawyers from 2014–2018. George’s work on the In re ODD Antitrust Litigation has been recognized by a number of legal publications and helped Winston be named the “2018 Antitrust Firm of the Year” by Benchmark Litigation US and the “2015 Team of the Year” in cartel defense by The Legal 500 US. 

Most recently, George was named a Fellow of the American Bar Foundation.

George is also actively involved in pro bono work; in addition to ongoing work in the field of voting rights and campaign finance reform, he recently helped obtain a landmark settlement against Immigration and Customs Enforcement, whose officers were alleged to have conducted a number of unconstitutional home raids.

Capabilities

Antitrust/Competition
Financial Services Litigation
Bankruptcy Litigation & Investigations
Restructuring & Insolvency
Class Actions & Group Litigation
Commercial Litigation & Disputes
Financial Services Transactions & Regulatory
Litigation/Trials
Securities, M&A & Corporate Governance Litigation
Technology Antitrust
Patent Litigation
Compliance Programs
Privacy & Data Security
Insurance Litigation
Health Care
Insurance
Financial Services
Cryptocurrencies, Digital Assets & Blockchain Technology
Retail & Luxury

Key Matters

  • City of Philadelphia, et al. v. Bank of America, et al. Counsel for Goldman Sachs & Co. in multi-billion dollar antitrust matter alleging that competitor banks conspired to fix interest rates for municipal bonds
  • Sizemore et. al. v. Zhao et al. As lead counsel for Defendant Binance US, obtained complete dismissal for in massive class action alleging securities laws violations arising from sale and promotion of digital assets
  • Licht v. Binance Holdings Ltd. et al. and Gonzalez v. Binance Holdings Ltd. et al. Lead counsel for Defendant Binance US in two civil RICO actions alleging involvement in so-called “pig butchering” schemes
  • Sjunde AP-Fonde v. Goldman Sachs & Co. LLC et al. Counsel for Goldman Sachs in high-profile Rule 10(b)(5) securities class action litigation
  • RIA R Squared v. DW Partners et al. Lead counsel in fraud and breach of contract action arising from three large commercial real estate transactions; successfully appealed dismissal of case brought by prior counsel
  • Azad v. Jenner. Represent Caitlyn Jenner and her manager in federal securities fraud and state law class action arising from sale and marketing of digital assets
  • In re Interest Rate Swaps Antitrust Litig. and Iowa Public Employees Retirement Assoc.et al. v. Bank of America Corp., et al. Counsel for defendant Goldman Sachs & Co. in two multi-billion-dollar antitrust putative class actions; obtained complete denial of class certification in Interest Rate Swaps matter
  • FM Global. COVID-19 litigations. Counsel for one of the world’s largest property and casualty insurers in over 12 litigations involving billions of dollars in claims for damages stemming from COVID-19 pandemic
  • Represent defendant in Title VII class action alleging religious discrimination arising from COVID-19 vaccination policy. Secured significant victories in several of those matters to date. 
  • MH Sub I et al. v. Muehter. Successfully enjoined defendant executive from joining competitor company for the entire term of his non-compete provision in restrictive covenant and misappropriation action
  • In re DBMP LLC; In re Aldrich Pump LLC, et al. Counsel for asbestos claimants creditors in proceedings arising out of separation of billions of dollars of asbestos liabilities from solvent companies’ assets
  • NYU Medical Center v. Factory Mutual Insurance Co. Argued and won summary judgment in US$1.6B claim arising out of damage caused by Superstorm Sandy; decision recently affirmed by the Second Circuit
  • Harmoni International Spice Corp. v. Bai, et al. Lead day-to-day counsel for plaintiff in high-stakes antitrust and civil RICO action against a cartel of foreign agricultural producers and their affiliates in the United States; argued and won Ninth Circuit appeal of district court dismissal
  • FCPA Investigation and Related Litigation. Represented major financial institution in multi-billion-dollar DOJ investigation along with follow-on derivative and class action securities litigation
  • In the Matter of Gladius Network LLC. Lead counsel for cybersecurity company in government investigation relating to digital assets; negotiated groundbreaking no-penalty settlement with SEC
  • In re Caesars Entertainment Operating Co. Counsel to Examiner in a massively complex investigation of 27 separate debt and real estate transactions involving billions of dollars
  • Financial Technology Investigations and Advice. Regularly advises financial technology companies in connection with compliance issues and regulatory proceedings involving digital assets and securities law
  • In re ODD Antitrust Litigation. Represented Panasonic Corp. in billion dollar antitrust class action alleging price fixing of optical disc drives. Helped lead joint defense group’s successful efforts to defeat motion for class certification, including briefing motions and overseeing expert phase of case
  • Omnicare v. United Healthcare, et al. Counsel in US$1.4B price-fixing and fraud action arising out of the merger between health care conglomerates United Healthcare and PacifiCare
  • Sheridan Healthcorp, Inc. v. Avmed, Inc. Obtained extremely favorable settlement for group of plaintiff anesthesiologists in federal and state monopolization actions against Florida HMO
  • Voting Rights Cases. Represented Common Cause NY, ACLU, and NYCLU in successful negotiations with New York State Board of Elections and Governor’s office regarding ballot access issues
  • Aguilar v. Immigration and Customs Enforcement. Trial counsel to group of families subjected to pre-dawn raids by ICE; helped obtain US$1M settlement and injunctive relief

Credentials

Education

George received a J.D. from Columbia Law School in 2002, where he was a member of the Human Rights Law Review and graduated as a Harlan Fiske Stone Scholar. He received an A.B. from Princeton University in 1999. In 2018, George graduated with distinction from Johns Hopkins University’s School of Advanced International Studies, where he focused on Strategic Studies and Conflict Management.

    Admissions
    • New York

    Related Insights & News

    Speaking Engagements

    • Co-panelist, “Corporate Rep Deposition Tips and Tricks,” ALM Complex Claims & Litigation Forum (February 2023)
    • Co-Moderator with Christine Edwards, “Setting the Stage: The Business Technology Climate in the Age of COVID-19,” Winston & Strawn's Disruptive Technologies Legal Summit (September 2020)

    Publications

    • Co-Author, “The SEC’s Approach to Digital Asset Regulation Harms Investors,” Bloomberg Law (March 2023)
    • Quoted, “Winston & Strawn Attorneys Back Digital Asset Association in Civil Crypto Fight,” The National Law Journal (March 2023)
    • Co-Author with Sofia Arguello and Patrick Opdyke, “Antitrust Concerns in No-Poaching, Wage-Fixing, and Non-compete Agreements,” LexisNexis (June 22, 2021)
    • Co-Author with Robert de By, “How to Avoid a Culture Clash in Business Mediations,” The Reporter (March 2007)
    Recognitions
    Winston Partners Featured on the 2025 Lawdragon 500 Leading Global Cyber Lawyers 2025

    May 7, 2025

    Blog
    Winston Musicians Win Judges’ Choice Award & Raise $37,000 for the LAFD Foundation at Law Rocks Battle of the Bands

    March 20, 2025

    Blog
    Winston Musicians Win Judges’ Choice Award & Raise $37,000 for the LAFD Foundation at Law Rocks Battle of the Bands

    March 20, 2025

    Speaking Engagement
    Ivan Poullaos Speaks on ANDA Litigation Strategies at 9th International IP Skills Summit

    March 6, 2025

    Recognitions

    Winston Attorneys Featured on the 2025 Lawdragon 500 Leading Global Antitrust & Competition Lawyers List

    January 30, 2025

    In the Media
    George Mastoris Discusses DOJ’s Antitrust Action Against Google With InformationWeek

    December 11, 2024

    Webinar
    How Will the U.S. Election Results Impact Your Financial Services Businesses and Clients?

    November 15, 2024

    Blog
    Banking Reform: An Increase In Scrutiny

    October 3, 2024

    Seminar/CLE
    Winston & Strawn Hosts Leadership and Communication Workshop with Internationally Acclaimed Author and Neuroscientist

    October 1, 2024

    Recognitions
    Winston & Strawn Recognized in The Legal 500 U.S. 2024

    June 12, 2024

    Recognitions
    Winston Attorneys Recognized in the Inaugural Edition of the Lawdragon 500 Leading Global Cyber Lawyers

    April 29, 2024

    Client Alert
    Landmark Decision in SEC v. Ripple Labs: Digital Assets Are Not Inherently Securities

    July 17, 2023

    View All Insights & News

    Capabilities

    Antitrust/Competition
    Financial Services Litigation
    Bankruptcy Litigation & Investigations
    Restructuring & Insolvency
    Class Actions & Group Litigation
    Commercial Litigation & Disputes
    Financial Services Transactions & Regulatory
    Litigation/Trials
    Securities, M&A & Corporate Governance Litigation
    Technology Antitrust
    Patent Litigation
    Compliance Programs
    Privacy & Data Security
    Insurance Litigation
    Health Care
    Insurance
    Financial Services
    Cryptocurrencies, Digital Assets & Blockchain Technology
    Retail & Luxury
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