Ketchum v. Duncan was a United States Supreme Court case that addressed the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner who was being held in federal custody. The case arose when the petitioner, Ketchum, was arrested and charged with a federal crime. He was then held in federal custody pending trial. Ketchum then filed a petition for a writ of habeas corpus in a state court, seeking to be released from federal custody. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner who was being held in federal custody. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the authority to interfere with the federal government's power to detain a prisoner. The Court also noted that the writ of habeas corpus was a fundamental right, and that the federal government had the exclusive power to protect this right. In conclusion, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner who was being held in federal custody. The Court reasoned that the writ of habeas corpus was a federal prerogative, and that the state court did not have the authority to interfere with the federal government's power to detain a prisoner.

Justice Field delivered the dissenting opinion in Ketchum v. Duncan, arguing that the court should have dismissed the writ of error for lack of jurisdiction. He argued that a state statute could not be challenged on constitutional grounds unless it was first determined to be unconstitutional by a state court and then appealed to the Supreme Court. The plaintiff had failed to do this, instead bringing their case directly before federal courts without any prior adjudication at all. Justice Field further noted that even if there were sufficient cause for granting certiorari, he would still dissent from reversing or modifying the judgment below because it did not appear from either party's brief or argument that any substantial federal question was involved in this case; thus no basis existed upon which they could reverse or modify said judgment as per Article III Section 2 Clause 1 of US Constitution.