Ex parte Pargoud 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, Pargoud, was held in federal custody in Louisiana and sought a writ of habeas corpus from the state court. 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 the writ of habeas corpus. 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 be allowed to interfere with the federal government's power to protect this right. The Court's decision in Ex parte Pargoud established that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in federal custody. This decision has been cited in numerous cases since then, and has been used to support the idea that the federal government has the power to protect the fundamental right of habeas corpus.

In Ex Parte Pargoud, the Supreme Court of the United States ruled that a state court had no authority to issue an injunction restraining a federal officer from performing his official duties. The majority opinion held that such action was beyond the scope of state power and violated Article III, Section 2 of the Constitution which grants exclusive jurisdiction over cases involving public officers acting under federal law to federal courts. However, Justice Field dissented from this ruling on two grounds: firstly, he argued that Congress had not granted any special privileges or immunities to persons holding office in either branch of government; secondly, he contended that it was within states' rights to protect their citizens against unconstitutional acts by those holding office in either branch. He further noted that if Congress wished for such protection then they should pass legislation granting it explicitly rather than relying on judicial interpretation alone.