Ex parte Slayton 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 who was being held in a federal prison. The case arose when a prisoner, Slayton, was held in a federal prison in the state of Missouri. Slayton sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. 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 held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals. The Court also noted that the state court's decision was in conflict with the federal government's exclusive authority to imprison individuals. 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 held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals.

In Ex Parte Slayton, the Supreme Court was asked to decide whether a writ of habeas corpus should be granted in order for an individual to challenge his detention by military authorities. The majority opinion held that the writ could not be issued because it would interfere with the power of Congress and President Lincoln during wartime. Justice Field dissented from this decision, arguing that while Congress had given broad powers to the executive branch during war time, these powers did not extend so far as to deny individuals their right under habeas corpus. He argued that if such a denial were allowed then any citizen could potentially be deprived of their liberty without due process or judicial review. Furthermore, he noted that even in times of war there must still exist some form of protection against arbitrary arrests and detentions which can only come through access to habeas corpus proceedings.