Ex parte Hughes 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 federal custody. The petitioner, John Hughes, was a prisoner in the custody of the United States Marshal for the District of Columbia. He had been convicted of a crime in the District of Columbia and was serving a sentence in the federal penitentiary. Hughes sought a writ of habeas corpus from the Supreme Court of the District of Columbia, claiming that his conviction was unconstitutional. The Supreme Court of the District of Columbia granted the writ, and the United States Marshal brought Hughes before the court. The United States Attorney then filed a motion to quash the writ, arguing that the state court did not have the authority to issue a writ of habeas corpus to a prisoner in federal custody. The Supreme Court of the District of Columbia denied the motion, and the United States appealed to the Supreme Court of the United States. The Supreme Court of the United States held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner in federal custody. 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 a person convicted of a federal crime. The Court also noted that the writ of habeas corpus was a remedy that could only be granted by a federal court. Therefore, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner in federal custody.

In Ex Parte Hughes, the Supreme Court was asked to decide whether a state court had jurisdiction over an action brought by a non-resident against another non-resident. The majority opinion held that it did not have such jurisdiction because there were no contacts between the parties and the forum state sufficient to support personal jurisdiction. Justice Field dissented from this decision, arguing that due process requires only minimal contact with the forum state in order for its courts to exercise personal jurisdiction over non-residents. He argued that even if there is no physical presence of either party within the forum state, as long as they are doing business or engaging in activities related to their dispute within its borders then it should be enough for them both to be subject to suit in those courts. He further noted that since neither party objected when service of process was made upon them outside of their home states, they had effectively consented and waived any objections based on lack of minimum contacts with respect to venue or jurisdictional issues.