Ex parte Cockcroft 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, Cockcroft, was held in federal custody in the state of Texas. Cockcroft sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. The federal government argued that the state court did not have the authority to issue the writ, as the federal government had exclusive jurisdiction over the prisoner. 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 federal government had exclusive jurisdiction over the prisoner, and that the state court did not have the authority to interfere with the federal government's authority. The Court also noted that the writ of habeas corpus was a federal remedy, and that the state court did not have the authority to issue such a remedy. The Court concluded that the state court did not have the authority to issue the writ of habeas corpus to the prisoner.

In Ex Parte Cockcroft, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving an alleged violation of federal law. The majority opinion held that the state court did not have jurisdiction because it lacked authority to enforce federal laws. However, Justice Field dissented from this decision and argued that the state courts should be allowed to exercise their own discretion in deciding whether or not they could hear cases involving violations of federal law. He noted that there were many instances where such decisions would be appropriate and beneficial for both parties involved in litigation as well as for society at large. Furthermore, he argued that allowing states to make these decisions would help ensure uniformity among different jurisdictions when dealing with similar issues under federal law. Ultimately, Justice Field concluded by stating his belief that Congress should provide clear guidance on how such matters should be handled so as to avoid any confusion or uncertainty about which court has jurisdiction over certain types of cases involving violations of federal laws.