Mark is Co-Managing Partner of Washington DC and focuses on white collar, securities, anti-corruption, and other regulatory enforcement investigations and related litigation matters.

He has represented clients in various industries, and regularly works on matters before the Securities and Exchange Commission, Department of Justice, CFTC, FINRA, FTC, IRS, and other Government agencies. 

Mark previously served as an Assistant United States Attorney in the United States Attorney' s Office for the Southern District of New York and as Assistant Chief Litigation Counsel in the SEC' s Division of Enforcement in Washington. As a federal prosecutor, Mark served as lead prosecutor and trial counsel on a number of high-profile cases, and also argued appeals before the United States Court of Appeals for the Second Circuit. Mark served in the Office' s Organized Crime Unit, where he prosecuted cases under the Racketeer Influenced and Corrupt Organizations Act ("RICO" ), and various fraud statutes; he also served as part of the Office' s Mortgage Fraud Task Force created in the wake of the financial crisis in 2008. 

For his work as a prosecutor, the United States Attorney General awarded Mark with the John Marshall Award for Trial of Litigation in 2011, and in 2010, Mark was awarded the Federal Law Enforcement Foundation' s Prosecutor of the Year Award. 

While at the SEC, Mark played a leadership role in numerous significant SEC enforcement investigations, cases, and settlements, including enforcement actions targeting accounting fraud, offering fraud, CDOs, pump-and-dump schemes, and insider trading. 

In addition, Mark was a member of the SEC' s Cross-Border Working Group and played a key role in investigations and litigations targeting accounting fraud at China-based issuers, addressing the cross-border issues presented by such government investigations.

Prior to his Government service with the Department of Justice and the Securities and Exchange Commission, following law school, Mark served as a law clerk to Chief Judge Edward R. Korman on the United States District Court for the Eastern District of New York, and as a law clerk to Judge Reena Raggi on the United States Court of Appeals for the Second Circuit.


Representative matters

Government and Regulatory Investigations

Multiple financial institutions in recordkeeping investigations and resulting resolutions before the SEC and CFTC.

Multiple financial institutions in non-public CFTC investigations into aspects of the credit default swaps market.

Multiple public companies in non-public SEC investigations following the completion of de-SPAC transactions regarding claims made in proxy statements, each of which has resulted in a non-public declination.

Pro bono

Conducted bi-annual trainings for prosecutors at the International Criminal Court in the Hague, along with a team of A&O Shearman partners, on various issues of trial strategy and examination technique.

Represented the heirs of journalist Marie Colvin in litigation against the Government of Syria under the Foreign Sovereign Immunities Act for extrajudicial killing, resulting in a $300 million judgment being entered in favor of our clients.

Representing an incarcerated individual on a pending habeas appeal before the D.C. Circuit raising considerable Brady issues discovered years after conviction.

Published Work

  • Lanpher, Mark and Schwartz, Adam, (2023) “SEC Investigations and Enforcement Actions”, Chapter 14: Securities Litigation: A Practitioner’s Guide, PLI Press
  • Lanpher, Mark, (2016) “‘Litvak’ Dicta Provides Counsel Fodder for Challenging Proof of Intent”, New York Law Journal
  • Lanpher, Mark, (2015) “Broken Windows: SEC’s Controversial Enforcement Philosophy Yields Record Results in 2014”, Bloomberg BNA Securities Regulation & Law Report
  • Lanpher, Mark, (2013) “New SEC Admission Policy May Be Tested Sooner Than Later”, Law360 Expert Analysis

Speaking Engagements

  • Panelist, ACI’s 3rd National Forum on Securities Litigation & Enforcement, February 2014
  • Panelist, ACI’s 18th National Forum on D&O Liability, October 2014


  • Recognized as a “Future Star” by Benchmark Litigation in its 2015–2022 editions.



New York, 2004

District of Columbia, 2013


New York Court of Appeals, 2004

United States District Court for the Southern District of New York, 2008

United States Court of Appeals for the Second Circuit, 2010

United States Court of Appeals for the Fourth Circuit, 2013

District of Columbia Court of Appeals, 2013

United States District Court for the District of Columbia, 2016

United States Tax Court, 2016

United States Supreme Court, 2019


B.A., magna cum laude, Yale University, 2000, Phi Beta Kappa

J.D., cum laude, Harvard Law School, 2003

A&O Shearman was formed on May 1, 2024 by the combination of Shearman & Sterling LLP and Allen & Overy LLP and their respective affiliates (the legacy firms). Any matters referred to above may include matters undertaken by one or more of the legacy firms rather than A&O Shearman.