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Mark Nielsen

Work (202) 861-5429
Groom Law Group

Work Department

Litigation, Health and Welfare, Fiduciary Responsibility


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.

For more information, please visit Mr. Nielsen's bio at: 


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.


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.

United States: Labor and employment

ERISA litigation

Within: ERISA litigation

Groom Law Group’s Washington DC-based ERISA litigation team is involved in class actions and other complex litigation involving plan sponsors, financial services firms, investment managers, actuaries and other service providers. The ‘utterly unflappable, confident and knowledgeable’ Lars Golumbic heads the practice group, which also includes Michael Prame, who is rated for his ‘substantial knowledge in the field and ability to understand the bigger picture’. Sarah Adams and Mark Nielsen are defending Financial Engines and a number of welfare plan trustees in breach of fiduciary duty class action suits, while a team including Edward Meehan and associate Samuel Levin represented a multi-employer pension fund in a withdrawal liability arbitration valued in excess of $100m. The team is also noted for its ESOP litigation expertise.

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