After law school, Gregory Sisk entered into public service, serving in all three branches of the federal government: legislative assistant to a United States Senator, law clerk to a judge on the United States Court of Appeals for the Ninth Circuit, and appellate specialist with the United States Department of Justice. Subsequent to government service, he was the head of the appellate department for a Seattle law firm. As an appellate attorney, Sisk has handled appeals cases before ten of the thirteen federal courts of appeals and several state appellate courts. Sisk joined the faculty of the Drake University Law School in 1991, where he was appointed the Richard M. & Anita Calkins Distinguished Professor.

Sisk is also the author of a novel, Marital Privilege published in 2014 by North Star Press, which is a legal drama with a law professor, lawyers, and judges as characters and which is set in the Twin Cities.

Sisk is a nationally-recognized scholar on the subjects of civil litigation with the federal government and empirical (statistical) analysis of judicial decision making; he also writes about federal courts, legal ethics, and constitutional law. He is the author of the casebook, “Litigation With the Federal Government,” which is published by Foundation Press, and a treatise by the same name, which is published by ALI-ABA. Sisk's empirical work on court decisions was honored with the Article Prize from the Law and Society Association in 1999.

He has remained an active member of the practicing bar, primarily in appellate litigation and as an expert witness or consultant on legal ethics. In recent years, he has briefed cases before the U.S. Supreme Court on civil suits against the federal government and jurisdiction in the Court of Federal Claims. He served as reporter for the Iowa Rules of Professional Conduct Drafting Committee appointed by the Iowa Supreme Court to draft the new set of ethics rules to govern lawyers in Iowa. Sisk also is an elected member of the American Law Institute.

Litigation With the Federal Government (West Academic Press, forthcoming 2016)

Litigation With the Federal Government: Cases and Materials (with Teacher's Manual) (Foundation Press, 2000) (2d ed., 2008) (2024 Update)

Marital Privilege (A Novel) (North Star Press, 2014)

“Too Many Notes”? An Empirical Study of Advocacy in Federal Appeals 12 Journal of Empirical Legal Studies 578 (2015)

The Legal Ethics of Real Evidence: Of Child Porn on the Choirmaster's Computer and Bloody Knives Under the Stairs 89 Washington Law Review 819 (2014)

Twilight for the Strict Construction of Waivers of Federal Sovereign Immunity 92 North Carolina Law Review 1245 (2014)

Muslims and Religious Liberty in the Era of 9/11: Empirical Evidence From the Federal Courts 98 Iowa Law Review 231 (2012) (with Michael Heise)

Ideology “All the Way Down”? An Empirical Study of Establishment Clause Decisions in the Federal Courts 110 Michigan Law Review 1201 (2012) (with Michael Heise)

The Jurisdiction of the Court of Federal Claims and Forum-Shopping in Money Claims Against the Federal Government 88 Indiana Law Journal 83 (2012)

The Dynamic Attorney-Client Privilege 23 Georgetown Journal of Legal Ethics 201 (2010) — Cited in Gillard v. AIG Ins. Co. 15 A.3d 44, 58 (Pa.)