Ex parte Bain was a United States Supreme Court case that dealt with the issue of whether a state court could issue a writ of habeas corpus to a prisoner who was being held in federal custody. The case arose when a prisoner, Bain, was arrested in the state of Georgia and held in federal custody. The state court issued a writ of habeas corpus, ordering the federal government to produce Bain in court. The federal government argued that the state court did not have the authority to issue the writ, as the federal government had exclusive jurisdiction over the prisoner. The Supreme Court held that the state court did not have the authority to issue the writ of habeas corpus. The Court reasoned that the federal government had exclusive jurisdiction over the prisoner, and that the state court did not have the power to interfere with the federal government's authority. The Court also noted that the writ of habeas corpus was a remedy for state prisoners, and that the federal government was not bound by the state court's writ. The Court concluded that the state court did not have the authority to issue the writ of habeas corpus, and that the federal government had exclusive jurisdiction over the prisoner.

In Ex Parte Bain, the Supreme Court was asked to decide whether a writ of habeas corpus should be issued in order for an individual to be released from custody. The majority opinion held that the writ could not issue because it would interfere with a state court's jurisdiction over criminal matters. Justice Field dissented, arguing that the power of federal courts to issue such writs is inherent and cannot be taken away by Congress or any other branch of government. He argued further that if this power were denied, then individuals who had been wrongfully arrested and detained would have no recourse against their captors since they could not appeal directly to federal courts for relief. Furthermore, he noted that denying access to habeas corpus proceedings would violate due process rights as guaranteed under both state and federal constitutions. Ultimately, Justice Field concluded that allowing states exclusive control over criminal matters did not preclude federal courts from issuing writs when necessary in order protect citizens' constitutional rights.