Ex parte French 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, William French, was held in federal custody in the state of Missouri. French sought a writ of habeas corpus from the state court, which the court granted. The federal government then 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 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 state court should not be allowed to interfere with the federal government's power to protect the rights of its citizens. 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 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 state court should not be allowed to interfere with the federal government's power to protect the rights of its citizens.

In Ex Parte French, the Supreme Court was asked to determine whether a writ of habeas corpus should be issued in favor of William French. The majority opinion held that the writ should not issue because it would interfere with state proceedings. However, Justice Field dissented from this ruling and argued that federal courts have jurisdiction over cases involving prisoners who are unlawfully detained by state authorities. He further stated that when a prisoner is being deprived of his liberty without due process of law, he has an absolute right to seek relief through habeas corpus regardless if there are pending criminal charges against him or not. Furthermore, Justice Field noted that Congress had granted federal courts exclusive power to issue such writs and thus they must exercise their authority whenever necessary for justice's sake.