Chelsea Cosillos - McDermott Will & Emery


Chelsea Cosillos is a litigator who focuses her practice on complex commercial matters in federal and state courts and arbitration proceedings, including class action and appellate cases.  Across a variety of industries, she has represented clients in disputes involving ERISA, antitrust, fraud, breach of contract, product liability, breach of fiduciary duty, and securities claims.

Chelsea also maintains an active pro bono practice, with an emphasis on immigration and criminal appeal matters.


  • Representing a major health insurer in a variety of matters, including cases involving ERISA, fraud, breach of contract, and antitrust claims.
  • Obtained complete victory on behalf of a major health insurer against multiple hospitals alleging improper reimbursement of certain out-of-network emergency services claims; successfully narrowed the hospitals’ causes of actions through multiple rounds of motions to dismiss and defeated the hospitals’ remaining statutory claim at summary judgment on the eve of an anticipated two-week federal jury trial in the Southern District of Florida.

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  • Empire State Counsel Program Honoree, 2018


Harvard Law School, JD, 2018
Arizona State University, BS, summa cum laude, 2013

New York