Mark Nielsen > Groom Law Group, Chartered > Washington DC, United States > Lawyer Profile

Groom Law Group, Chartered
United States




Mark’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 regularly represents plans, their sponsors, and insurance companies before federal and state regulatory agencies.

As a litigator, he has successfully defended plan trustees and plan sponsors in federal court against breach of fiduciary duty and prohibited transaction claims brought by the Department of Labor and plan participants and beneficiaries. These claims involved 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.

In addition, Mark regularly counsels plans, plan trustees, and plan sponsors as to their fiduciary obligations under ERISA. These include 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 Age Discrimination in Employment Act.

Mark previously served as a member of the firm’s Executive Committee.


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


  • 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


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

Lawyer Rankings

United States > Labor and employment > ERISA litigation

Groom Law Group, Chartered focuses its attention on the defense of ERISA class actions, including those relating to breach of fiduciary duties, 401(k) excessive fee and investment strategy, employer stock, defined pension plans, actuarial equivalence. The practice is led by Lars Golumbic and William Delany: Golombic is well-regarded for his involvement in class actions involving plan sponsors and fiduciaries and service providers as well as DOL investigations and enforcement matters, while Delany shares this focus along with Michael Prame, advising on ERISA class actions regarding plan administration, stock drops and fiduciary duties. Mark Nielsen has represented insurance companies and health plan sponsors in cases relating to fiduciary duties and defective COBRA notices and Sarah Adams concentrates on class actions and government investigations, litigating on behalf of plan sponsors, fiduciaries facing allegations of ERISA violations, focusing on ESOPs, imprudent investment, actuarial malpractice and church plan putative class actions. Samuel Levin and Edward Meehan are also key contacts within the practice. All named lawyers are based in Washington DC.