Ex parte Clarke is 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 Clarke, was held in federal custody in the state of New York. Clarke sought a writ of habeas corpus from the state court, arguing 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 federal custody. The Court reasoned that the writ of habeas corpus was a federal power, 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 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 power, 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 interfere with the federal government's power to protect the rights of its citizens.

In Ex Parte Clarke, the Supreme Court was asked to decide whether a writ of habeas corpus should be issued in order for an individual to challenge their detention. The majority opinion held that the writ could not be issued because it would interfere with military operations during wartime. Justice Field dissented from this decision and argued that Congress had granted individuals the right to challenge their detentions through habeas corpus proceedings, regardless of any war-related considerations. He further noted that if such challenges were denied then citizens' rights would be violated without due process or judicial review. Field concluded by asserting that denying access to habeas corpus proceedings undermined fundamental principles of justice and liberty which are essential components of our constitutional system.