Sam Callahan focuses on appellate and complex civil litigation in state and federal courts. He has argued cases in multiple federal courts of appeals; represented parties at the certiorari and merits stages in the US Supreme Court; and successfully briefed cases raising high-stakes issues of constitutional interpretation, administrative law, and criminal procedure, among others. 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 addition of 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.


  • Major property developer in securing unanimous affirmance of agency decision authorizing $200 million community redevelopment project in Georgetown. DC Preservation League v. Mayor’s Agent for Historic Preservation, 236 A.3d 373 (D.C. 2020).
  • 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 successful Ninth Circuit appeal involving Medicare statutes. Secured pathbreaking decision holding that medical service providers can sue health plans for discriminating against patients needing dialysis. DaVita Inc. v. Virginia Mason Memorial Hospital, 981 F.3d 679 (9th Cir. 2020).
  • The Bolivarian Republic of Venezuela in several cases involving interpretation of Foreign Sovereign Immunities Act.
  • Criminal defendant in briefing and arguing successful Fourth Circuit appeal asserting ineffective assistance of trial counsel. Convinced court to vacate dismissal of § 2255 petition and to order evidentiary hearing regarding trial counsel's failure to seek suppression of un-Mirandized statements. United States v. Pressley, 990 F.3d 383 (4th Cir. 2021).
  • Individual attorney in pending Fifth Circuit appeal challenging authority of federal agents to search electronic devices at border and at international airports without a warrant.
  • Immigration-rights organizations at US Supreme Court in successful Administrative Procedure Act challenge to attempted addition of citizenship question to 2020 Census. Department of Commerce v. New York, 139 S. Ct. 2551 (2019).
  • Voters and political groups in successful partisan gerrymandering challenge to North Carolina's state legislative districts. Helped draft post-trial briefing that led to landmark decision under North Carolina constitution. Common Cause v. Lewis, No. 18-cvs-14001 (N.C. Super. Ct.).
  • The State of Oklahoma at US Supreme Court in case involving State's ability to prosecute major crimes on former Indian lands in eastern Oklahoma. McGirt v. Oklahoma, 140 S. Ct. 2452 (2020).
  • Criminal defense organizations as amici curiae at US Supreme Court in case about fabrication of evidence by law enforcement. Drafted amicus brief cited in 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 settlement requiring Department to stop enforcing policies.
  • Former Members of Congress and House General Counsels as amici curiae in several cases at US Supreme Court and federal appellate courts involving separation of powers, including Trump v. Mazars USA, LLP, 140 S. Ct. 2019 (2020); Trump v. Sierra Club, No. 20-138; 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

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