Ex parte Fisk was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The case arose when a prisoner, Fisk, was held in federal custody in the state of California. Fisk sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. The federal government argued that the state court did not have the authority to issue such a writ, as the federal government had exclusive jurisdiction over federal prisoners. The Supreme Court ultimately held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. The Court reasoned that the federal government had exclusive jurisdiction over federal prisoners, and that the state court did not have the authority to interfere with the federal government's authority. The Court also noted that the writ of habeas corpus was a remedy available only to those held in state custody, and not to those held in federal custody. As such, the state court did not have the authority to issue a writ of habeas corpus to Fisk.

In Ex Parte Fisk, the Supreme Court was asked to determine whether a writ of habeas corpus should be issued for one George W. Fisk who had been convicted in an Illinois state court and sentenced to prison for larceny. The majority opinion held that the writ should not issue because there were no facts presented which would show that Fisk's conviction violated federal law or his constitutional rights. Justice Field dissented from this ruling, arguing that since it was unclear if any evidence existed which could have exonerated him at trial, he deserved a chance to prove his innocence before being sent away unjustly. He argued further that even though the petitioner may not have stated sufficient grounds on which relief could be granted, it did not mean he was necessarily guilty and thus denied due process of law by having no opportunity to present exculpatory evidence in support of his defense.