associate justice of the United States Supreme Court (1790–99).

At the age of 17 Iredell was appointed comptroller of the customhouse at Edenton, N.C., to which his father, formerly a Bristol merchant, had migrated. He studied law and became active in the American cause. Although hopeful as late as June 1776 for a reconciliation with Britain, he worked as one of the commissioners to draft and revise the laws of the new state of North Carolina. He served briefly as a superior-court judge and as state attorney general and, in 1787, was charged by the legislature to codify the state's statutes; “Iredell's Revisal” appeared in 1791.

He was a leader of the North Carolina Federalists in supporting ratification of the Constitution, and his letters in its defense (published over the name Marcus) are said to have prompted President George Washington to appoint him to the U.S. Supreme Court. He was the original court's youngest member.

Iredell's opinion in Calder v. Bull (1798) helped establish the principle of judicial review five years before it was actually tested in Marbury v. Madison. He is, however, remembered primarily for his dissents, most notably that in Chisholm (Chisholm v. Georgia) v. Georgia (1793), which maintained that an action of assumpsit could lie against a state only by authority of the Constitution, thus lending weight to the campaign for the 11th Amendment.

Iredell's health failed less than 10 years after his appointment, in large part as a result of the travel and strain of holding circuit courts, which at the time was required of Supreme Court justices.