“He provides practical and strategic advice that reflects commercial realities. [He] is extraordinarily talented.” (2022)

“[A] top-flight white-collar lawyer” and “an outstanding trial lawyer.” (2020)

Chambers USA


Greg Deis is a former Assistant U.S. Attorney who currently serves as global co-chair of Mayer Brown's Global Investigations & White Collar Defense practice and co-leader of Mayer Brown’s Litigation & Dispute Resolution Practice in Chicago. Greg regularly represents clients in high-stakes criminal and regulatory investigations and complex civil litigation. A Fellow of the American College of Trial Lawyers, Greg is a seasoned trial lawyer, having served as lead trial counsel in numerous civil and criminal trials and arbitrations.

Greg has been recognized as a leading lawyer by Chambers USA since 2019. In Chambers USA 2021 clients note that he is "super personable, good in court and…an excellent investigator – a truly terrific lawyer” with an “incredible balance of intelligence and patience – he exudes calmness." Greg is also recognized in Legal 500 USA with one client commenting: “Greg Deis is a standout. A skilled advocate and counselor.” Lawdragon 500 has also recognized Greg as a leading litigator in the U.S.

Greg regularly represents corporate and individual clients in investigations led by the US Department of Justice, the US Securities and Exchange Commission, the Commodity Futures Trading Commission, state attorneys general and other US and foreign regulators. These matters have involved various areas of the law, including the FCPA and domestic corruption statutes, federal securities laws, US sanctions, the False Claims Act, antitrust, customs, tax, money laundering and environmental offenses.

Greg's complex litigation experience focuses on trial work and includes cases involving class actions, RICO, the Sherman Act, federal and state securities law, the Lanham Act, products liability, accounting malpractice, breach of contract, BIPA, tortious interference with contract and environmental law.

Prior to rejoining Mayer Brown in 2013, Greg served as an Assistant US Attorney in Chicago, assigned to the Public Corruption section. Greg prosecuted numerous public officials and law enforcement officers with bribery, extortion, fraud and tax offenses, including the prosecutions of multiple Illinois state representatives. In addition to his corruption experience, Greg investigated and prosecuted a wide range of federal criminal cases involving complex financial fraud, money laundering, computer offenses and international drug trafficking, including prosecutions of numerous high-ranking members of the Los Zetas and Sinaloa cartels.

Greg maintains an active pro bono practice, including serving as a panel attorney for the Federal Defender Program in Chicago, representing indigent defendants in federal criminal proceedings. Greg serves on the board of directors of Legal Aid Chicago and the Federal Bar Association’s Chicago Chapter, and is a member of the Chairmen’s Advisory Council of Big Shoulders Fund. He has been an adjunct professor of criminal procedure and trial advocacy at DePaul University College of Law and previously served on Law360's White Collar Editorial Advisory Board.

Greg began his legal career as a law clerk for the Honorable Deanell Reece Tacha, Chief Judge of the US Court of Appeals for the Tenth Circuit.

Securities Investigations: Internal, Civil and Criminal


Representative experience includes:

White Collar Defense

  • Electric vehicle manufacturer in DOJ and SEC investigations relating to allegations concerning revenue recognition, public disclosures and insider trading; SEC investigation closed with no action.
  • Represent Fortune 50 company, former senior officer of Fortune 100 subsidiary and several members of Illinois General Assembly in DOJ investigation of alleged public corruption focused on former Illinois House Speaker Michael Madigan.
  • Large food manufacturer in DOJ Antitrust criminal investigation focused on alleged price fixing in connection with USDA bid.
  • Technology company in DOJ Antitrust investigation; DOJ closed investigation with no action against client.
  • Fortune 500 medical device company in a parallel DOJ civil/criminal False Claims Act investigation; DOJ declined to intervene.
  • Fortune 50 financial institution in a DOJ investigation involving allegedly abusive tax shelters; no charges against client.
  • Fortune 50 company in an SEC investigation regarding alleged accounting fraud; obtained no action letter following Wells submission.
  • Fortune 500 company in OFAC/BIS investigation relating to product sales to Iran; BIS investigation resolved with no monetary penalty.
  • Fortune 50 company in DOJ investigation of public corruption allegations.
  • Fortune 500 company in DOJ investigation relating to allegedly illegal campaign contributions.
  • Fortune 500 financial institution in DOJ investigation and parallel civil litigation arising out of fraud on financial institution by purported private equity fund.
  • Alleged tippee/tipper in DOJ and SEC insider trading investigation arising out of Equifax data breach; DOJ and SEC investigations closed with no charges.
  • Proprietary trading firm in multiple DOJ spoofing prosecutions.
  • Trading firm in CFTC investigation of alleged manipulative trading practices; CFTC closed its investigation with no action.
  • Construction company in an Illinois Attorney General's Office consumer fraud investigation.
  • Fortune 500 company in a Texas Attorney General's Office consumer fraud investigation.
  • Public international hotel group in connection with a DOJ and internal investigation of a terrorist attack in Mali.
  • Oil-and-gas company in a DOJ criminal environmental investigation.
  • Private equity client in a DOJ AML investigation arising out of alleged bribery and money laundering in Peru.
  • Senior engineer in the DOJ’s GM ignition switch investigation.
  • Senior engineer in the investigations by the DOJ and German prosecutors into Audi emissions.
  • Former senior finance executive of Fortune 500 healthcare company in SEC investigation arising out of $250 million restatement relating to allegedly improper foreign currency transactions.
  • Senior executive of Japanese company charged by DOJ Antitrust with alleged price fixing relating to computer components.
  • Former Big 4 partners in SEC investigation of alleged violation of audit independence rules.
  • CEO of Fortune 100 subsidiary in DOJ public corruption investigation. 
  • High-ranking member of Illinois General Assembly in DOJ public corruption investigation.
  • Fortune 500's former general counsel in an SEC investigation regarding alleged accounting fraud.
  • Fortune 50 joint venture's general counsel in a DOJ/SEC FCPA investigation of alleged improper payments in India.
  • Fortune 50 senior executive in a DOJ and SEC FCPA investigation regarding alleged improper payments in Brazil.
  • Fortune 500's former general counsel in a DOJ/SEC FCPA investigation regarding alleged improper payments in Brazil.
  • Registered broker in CFTC and DOJ investigation of fraud and unauthorized trading.
  • Numerous hospital executives, including CFO, in a DOJ False Claims Act investigation arising out of a hospital-physician joint venture.
  • Steel distributor in an SFO investigation involving alleged financial fraud.
  • Public accounting/consulting firm in numerous DOJ criminal/civil investigations, involving alleged bank fraud, AML/BSA violations and False Claims Act claims.
  • International PR firm's CFO in a DOJ FCPA investigation regarding alleged improper payments, travel and entertainment in China.
  • Private equity portfolio company officer in a parallel DOJ and SEC investigation of alleged securities fraud.
  • Physician and executive director in a parallel DOJ criminal and civil False Claims Act investigation.
  • Corporate executive in a successful Seventh Circuit appeal of a federal criminal sentence for conversion/embezzlement.

Internal Investigations

  • Internal investigation for a Fortune 500 company into whistleblower allegations of accounting fraud and securities law violations; SEC investigation closed with declination.
  • Investigation for Fortune 50’s Brazilian subsidiary arising out of Operation Car Wash.
  • Investigation for Fortune 50 Mexico subsidiary involving alleged improper payments in Mexico to customs officials and employees of a public health and safety inspector.
  • Investigation for Japanese multinational company’s US subsidiary into alleged commercial bribery in Indonesia.
  • Internal investigation for a Fortune 500 financial institution into whistleblower allegations of fraud in connection with rating foreign currency transactions involving New York, London and Hong Kong trading desks.
  • Internal investigation for a Fortune 50 company into public corruption allegations involving political contributions and state government contracts.
  • Internal investigation for a Fortune 500 company into alleged corrupt payments and entertainment through third-party intermediary in Japan.
  • Internal investigation for a Fortune 500 consumer goods company into allegations of OFAC Iran sanctions violations.
  • Investigation for a Fortune 500 subsidiary into whistleblower allegations of improper accounting at UK subsidiary.
  • Internal investigation for a public heavy equipment manufacturer into potential FCPA, antitrust, money laundering and US sanctions violations involving a non-US wholly-owned subsidiary and transactions in Egypt, India and Thailand.
  • Internal investigation for a public heavy equipment manufacturer into potential FCPA violations involving a wholly-owned subsidiary and transactions in the UAE.
  • Internal investigation for construction equipment supplier into allegations of commercial bribery and bid rigging through UK third-party intermediary for Netherlands-based project.
  • Internal investigation for metals fabricator involving alleged improper payments in Mexico to customs officials and employees of a public health and safety inspector.
  • Internal investigation for a processed food supplier into allegations of customs violations.
  • Internal investigation for a public energy company into allegations of conflicts of interest, undisclosed related-party transactions, misappropriation of corporate opportunities and antitrust violations, by the CEO and chairman of the board of directors.
  • Internal investigation for a national home improvements/furnishings provider into allegations of conflicts of interest, undisclosed related-party transactions and self-dealing by the CEO/board member.
  • Internal investigation for a public agency into allegations of CEO misconduct in awarding vendor contracts and conflicts of interest.
  • Internal investigation for a charter school operator involving alleged improper payment by a third-party vendor; represented client in related SEC and IG investigations.
  • Internal investigation for a public company into allegations of insider trading involving board of directors members.
  • Internal investigation for a Fortune 500 company into allegations that the CEO of the company's foreign subsidiary misappropriated trade secrets from a former employer.

Complex Commercial Litigation

  • Counsel for international accounting firm in two-week arbitration alleging malpractice in connection with financial statement audit, which related to a $25 million embezzlement that resulted in federal criminal charges against the audit client’s CEO; panel dismissed all claims against accounting firm, awarded damages on accounting firm’s counterclaim and assessed costs against claimant.
  • Counsel for a Big 4 accounting firm in an arbitration involving a former employee alleging tortious interference with contract and defamation; tribunal award in client’s favor dismissing all claims. 
  • Counsel for an AmLaw 20 international law firm in a two-week arbitration against a software developer; tribunal award in client's favor awarding maximum damages permitted under the contract. 
  • Counsel for an officer of a private equity portfolio company in a Delaware Chancery Court trial involving allegations of, inter alia, securities fraud; case settled following a multi-week trial. 
  • Counsel for two "affiliates" of Sprint in high-stakes trials challenging Sprint's conduct following the Sprint-Nextel merger. The clients obtained favorable judgments in two separate trials in Delaware and Illinois. In Illinois, the client secured an injunction requiring that Sprint cease operating its Nextel business in the client's territory. In Delaware, the client secured an injunction prohibiting Sprint from using Sprint trademarks to promote Nextel products in the client's territory. 
  • Counsel for a Fortune 50 financial institution in a RICO and fraud action; obtained summary judgment arguing successfully against direct fraud and respondeat superior liability.
  • Counsel for online insurance platform in Section 11 securities case arising out of company’s IPO.
  • Counsel for Fortune 50 subsidiary in ERISA suit.
  • Counsel for Fortune 100 company in fraud suit against private equity firm arising out of private equity firm’s acquisition of client’s supplier.
  • Counsel for public technology company in federal antitrust class action.
  • Counsel for a public energy company in a federal RCRA environmental action; obtained dismissal on 12(b)(6) grounds based on RCRA issues of first impression in the Seventh Circuit. 
  • Counsel for a public international hotel group in a federal suit seeking damages based on former Yugoslavia's nationalization of plaintiff's ancestors' property in present-day Serbia; obtained dismissal on forum non conveniens grounds.
  • Achieved dismissal of a Lanham Act claim arising out of a dispute between members of a joint venture, which the Seventh Circuit affirmed on appeal.
  • Achieved dismissal of a $110 million defamation suit brought by a former Illinois Appellate Court judge and candidate for the Illinois Supreme Court against a political action committee and several individuals. The trial court decision was affirmed by the Illinois Appellate Court and the Illinois Supreme Court.
  • Counsel for an online insurance platform in a federal Lanham Act case.
  • Counsel to public gaming company in proposed class action under Illinois BIPA statute.
  • Counsel to international public accounting firm in proposed class action alleging audit malpractice.
  • Counsel for a Fortune 50 financial institution in lawsuits filed around the US relating to allegedly abusive tax shelters.


University of Illinois College of Law, JD, summa cum laude
Order of the Coif, valedictorian

Marquette University, BS, Civil & Environmental Engineering


  • Illinois