John Marston

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Profile

Overview

John Marston is a courtroom-tested government enforcement attorney who has led numerous investigation matters and tried more than 50 civil and criminal cases to verdict. As a former federal prosecutor, he helps clients navigate—and defeat—high-stakes civil and criminal investigations and charges.

John works with clients across tax, bankruptcy, securities law, antitrust, national security, criminal law and other areas. His client work spans diverse industries, including accountancy and other professional services, sports and entertainment, life sciences, technology, finance, energy, shipping and nonprofits. John has particularly deep experience in federal income tax matters—civil and criminal—and regularly helps clients resolve complex tax issues with the IRS and Department of Justice.

Before joining Sheppard, John served as an assistant U.S. attorney in the Fraud and Public Corruption Section in Washington, D.C., where he conducted complex investigations involving tax, bankruptcy, finance, antitrust, healthcare and cybersecurity. His insider’s knowledge of the government's burden in prosecution informs how he counsels clients facing investigation, indictment or trial.

John also brings experience from his time as an associate in the tax controversy practice at an international law firm, where he litigated matters against the IRS and the Department of Justice in federal Tax Court and various U.S. District Courts. He collaborates regularly with Sheppard's Tax and Employee Benefits lawyers, giving clients the benefit of his understanding of tax issues alongside his prosecutorial background.

John views pro bono service as a way to apply his litigation skills to serve his community. For example, he successfully reversed all convictions in a 26-count case against a client in Prince George's County Circuit Court and has argued two pro bono appeals, including one as defense counsel in a double homicide case.

In his free time, John spends time with his wife and three children, and they frequently camp, fish, hike and enjoy powersports in the north woods of Minnesota.


Experience

Criminal Defense

  • Represented individual charged with federal weapons offense and obtained full dismissal of indictment.
  • Represented individual charged with federal weapons offenses and obtained sentence significantly below federal guidelines.
  • Represent former government employee in federal case involving multiple potential life-maximum charges.
  • Represented individual charged with federal drug offense and obtained sentence of time-served, which was significantly below federal guidelines.
  • Represented individual indicted on charges related to alleged government procurement fraud.
  • Represented individual under investigation by federal law enforcement agencies and the U.S. Attorney’s Office for the Southern District of New York - individual not charged.
  • Advised non-U.S. energy company in connection with SEC and DOJ investigations of a domestic company.
  • Defended individual charged with multiple felony offenses in Maryland, and obtained full reversal of convictions on appeal.
  • Defended individual on appeal from homicide conviction in Maryland.

Civil Tax Matters

  • Represent multiple partnerships in audits and Tax Court litigation involving the validity and value of conservation easement deductions.
  • Represent multiple individual investors in connection with IRS inquiries into conservation easement deductions.
  • Represent Big Four accounting firm as witness in multiple civil litigation matters.
  • Represented national shipping company in connection with its classification of workers as contractors, resulting in full concession by IRS while still in the audit phase.
  • Represented major financial institutions in litigation and trials related to the validity of hundreds of millions of dollars in claimed foreign tax credits.
  • Represented national retailer before IRS Appeals in connection with the validity of loss deductions from sales of stores, resulting in settlement of the dispute prior to litigation.
  • Represented multinational technology and pharmaceutical companies in responses to congressional inquiries concerning international tax matters, and prepared executives for potential testimony.
  • Member of team that tried estate tax case in U.S. Tax Court, resulting in complete victory for the taxpayer.
  • Represented substantial charity in IRS audit related to possible excess benefit transactions, resulting in no liability at the conclusion of the audit.
  • Represented individual before IRS to resolve tax debts.

Government Enforcement

  • Represent former hedge fund manager in tax investigation by New York Attorney General’s Office.
  • Represent company in grand jury investigation by DOJ Antitrust Division.
  • Represent accounting firm in grand jury investigation by DOJ Tax Division.
  • Represent multiple consulting firm employees and partners as witnesses in DOJ investigation.
  • Investigated home improvement contractor who had committed bankruptcy, welfare, and contracting fraud.
  • Investigated former employee of multinational investment bank on wire fraud, identity theft, tax evasion, and money laundering charges.
  • Investigated collision center manager who conspired with a U.S. Department of State employee to misappropriate government vehicles.
  • Investigated substantial international money-laundering case.
  • Investigated substantial data breach involving government website, which led to nearly $40 million in false tax returns; investigation resulted in money-laundering prosecutions in multiple districts.
  • Investigated former high-ranking D.C. government official with subscribing a false tax return.
  • Investigated false bomb and hostage-crisis threats called into the D.C. 911 system; identified perpetrator despite his use of deactivated phones and spoofed numbers.
  • Investigated congressional chief of staff on false statement charges.

Other Notable Experience

  • Opinion writer published by USA Today and The Hill.
  • Commentator featured on CNN and in articles published by Vanity Fair, CNBC and the New York Times.

Professional Experience 

  • United States Attorney’s Office, Assistant U.S. Attorney, Fraud and Public Corruption Section, Washington, D.C., January 2013 to April 2018
Credentials
Education

J.D., Cornell Law School, 2004, summa cum laude, Order of the Coif

B.A., Wheaton College, 1999, summa cum laude

Admissions

District of Columbia

New York

Virginia

U.S. Court of Appeals for the District of Columbia Circuit

U.S. District Court for the District of Columbia

U.S. District Court for the Eastern District of Virginia

U.S. District Court for the Western District of Virginia

U.S. District Court for the Southern District of New York

U.S. Tax Court

Honors

Distinguished Service Award, given by Special Agent in Charge, FBI and Inspector in Charge, USPIS

Special Achievement Award, given by U.S. Attorney

Best Lawyers in America, Criminal Defense: General Practice, Best Lawyers, 2026

Recipient of West Outstanding Scholastic Achievement Award and Kerr Memorial Prize, 2004

Memberships

Member, J. Edgar Murdock Inn of Court

Editor, Cornell Law Review

Thought Leadership
  • Panelist, "Significant Legal Developments in the Regions - Northeast Region," ABA's 38th National Institute on White Collar Crime, March 2023