Sam Callahan focuses on appellate and complex civil litigation in state and federal courts. He regularly represents individuals, businesses, and governments in the US Supreme Court and federal appellate courts, and has briefed and argued issues ranging from administrative law to sovereign immunity to novel questions of criminal law and procedure. Mr. Callahan also has significant experience with political and voting-rights litigation, having played key roles in successful challenges to North Carolina's gerrymandered legislative districts and to the Trump Administration's attempt to add a citizenship question to the 2020 Census.

Mr. Callahan joined the firm in 2018 after serving as a law clerk to the Honorable Paul V. Niemeyer of the United States Court of Appeals for the Fourth Circuit and the Honorable Christopher R. Cooper of the United States District Court for the District of Columbia. He is a magna cum laude graduate of Harvard Law School, where he served as an Executive Editor of the Harvard Law Review.


  • Immigration-rights organizations at the US Supreme Court in a successful challenge to the attempted addition of a citizenship question to the 2020 Census. Department of Commerce v. New York, 139 S. Ct. 2551 (2019).
  • Major property developer in securing unanimous affirmance of an agency decision that authorized a $200 million community redevelopment project in Georgetown. DC Preservation League v. Mayor's Agent for Historic Preservation, No. 19-AA-86 (D.C. Ct. App.).
  • Trade association at the DC Circuit in successfully staying novel emissions and fuel-consumption regulations imposed on trailers. Truck Trailer Manufacturers Association, Inc. v. EPA, No. 16-1430 (D.C. Cir.).
  • Major cruise lines in securing dismissal of over a dozen high-profile federal maritime lawsuits.
  • Dialysis provider in pending Ninth Circuit appeals involving a Medicare statute that prohibits health plans from discriminating against patients who need dialysis.
  • The Bolivarian Republic of Venezuela in several cases involving interpretation of the Foreign Sovereign Immunities Act.
  • Criminal defendants in multiple appeals involving interpretation of the US Sentencing Guidelines, the Fifth Amendment right against self-incrimination, and the Eighth Amendment prohibition on cruel and unusual punishment.
  • Individual attorney in a pending Fifth Circuit appeal challenging the authority of federal agents to search electronic devices at the border and at international airports without a warrant.
  • Voters and political groups in a successful partisan gerrymandering challenge to North Carolina's state legislative districts. Helped draft post-trial briefing that led to landmark decision under the North Carolina constitution. Common Cause v. Lewis, No. 18-cvs-14001 (N.C. Super. Ct.).
  • The State of Oklahoma at the US Supreme Court in a case involving the State's ability to prosecute major crimes on former Indian lands in eastern Oklahoma. McGirt v. Oklahoma, No. 18-9526.
  • Criminal defense organizations as amici curiae at the US Supreme Court in a case involving fabrication of evidence by law enforcement. Drafted an amicus brief that was cited in the majority opinion. McDonough v. Smith, 139 S. Ct. 2149 (2019).
  • Border-reform advocates in a challenge to Department of Homeland Security policies restricting photography at ports of entry. Secured a settlement requiring the Department to stop enforcing the policies.
  • Former Members of Congress and House General Counsels as amici curiae in several cases at the US Supreme Court and federal appellate courts involving the separation of powers, including Trump v. Mazars USA, LLP, 140 S. Ct. 2019 (2020); Trump v. Sierra Club, No. 19A60; and Committee on the Judiciary of the US House of Representatives v. McGahn, 968 F.3d 755 (D.C. Cir. 2020) (en banc).


  • JD, Harvard Law School, 2016, magna cum laude
  • BM, Trumpet Performance and BA, Economics, Indiana University, 2013, Phi Beta Kappa
  • District of Columbia
  • Maryland
  • US Court of Appeals for the First, Second, Third, Fourth, Fifth, Seventh, Ninth, and DC Circuits
  • US District Court, District of Columbia
  • US District Court, District of Maryland
  • US Court of Appeals for the Fourth Circuit, The Honorable Paul V. Niemeyer
  • US District Court, District of Columbia, The Honorable Christopher R. Cooper

Email Disclaimer