Groom Law Group, Chartered
1701 Pennsylvania Avenue, N.W.
Washington, DC 20006-5811

Related Info +
T: 202-861-5429
F: 202-659-4503


Related Information


  • LL.M., Labor and Employment Law, Georgetown University Law Center
  • Certificate of Specialization in Employee Benefits Law, Georgetown University Law Center
  • J.D., State University of New York at Buffalo
  • B.A., Highest Honors, Indiana University, Phi Beta Kappa 

Bar & Court Admissions

  • United States Supreme Court
  • Court of Appeals, Second Circuit
  • Court of Appeals, Ninth Circuit
  • U.S. District Court, District of Columbia
  • U.S. District Court, Northern District of Illinois
  • U.S. District Court, Eastern District of Michigan
  • District of Columbia
  • New York
Mark C. Nielsen
Mark C. Nielsen
"Employee benefits is such a complicated and multifaceted legal field—touching on everything from employment discrimination, to antitrust, and to securities laws—that I knew it was an area in which I would never stop learning." More from Mark's perspective

Mark C. Nielsen brings a broad array of experience to Groom's litigation, fiduciary responsibility, and health and welfare practice groups.  As a litigator, Mr. Nielsen has successfully defended plan trustees and plan sponsors in federal court against breach of fiduciary duty and prohibited transaction claims brought by the U.S. Department of Labor and plan participants and beneficiaries, including actions involving complex commercial real estate developments, stock option and stock repurchase programs, and multiple employer welfare arrangements.  He has also successfully defended plans and their fiduciaries in benefit claim disputes in both trial and appellate courts, and he has successfully defended employers against claims arising under the Americans with Disability Act. 

Mr. Nielsen's background includes a broad array of multijurisdictional and complex commercial disputes, including class action litigation.  He has practiced before state and federal courts, as well as in arbitration actions, and he has been involved in all aspects of litigation—from pretrial discovery and motion practice to trial advocacy and appellate practice.  He also regularly represents plans, their sponsors, and insurance companies before federal and state regulatory agencies.

In addition, Mr. Nielsen regularly counsels plans, plan trustees, and plan sponsors as to their fiduciary obligations under ERISA, including duties attendant to plan investments and transactions, as well as the requirements of federal and state health care laws, including Medicare Part D, HIPAA, COBRA, and the requirements of other laws, such as the Age Discrimination in Employment Act and federal labor laws.

Honors & Distinctions

  • Listed, The Legal 500 US, ERISA Litigation (2016-2017)
  • Listed, The Legal 500 US, Employee Benefits and Executive Compensation (2013)
  • Listed, The Legal 500 US, Healthcare (2012, 2014)
  • Chapter Editor, Employee Benefits Law

Previous Experience

  • Investigator with the Department of Labor's Employee Benefits Security Administration

Professional Affiliations

  • Vice Chair, Employee Benefits Committee, Bar Association of the District of Columbia
  • Co-Chair, Subcommittee on Welfare Plan Litigation, Employee Benefits Committee, American Bar Association