McCarthy v. Provost 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, McCarthy, was held in federal custody in the state of New York. The state court issued a writ of habeas corpus to the federal authorities, ordering them to produce McCarthy in court. The federal authorities refused to comply with the writ, arguing that the state court did not have the authority to issue such a writ. The Supreme Court held that the state court did have the authority to issue the writ of habeas corpus. The Court reasoned that the writ of habeas corpus was a fundamental right that could not be denied by the federal government. The Court further held that the state court had the authority to issue the writ, as long as the prisoner was held in the state. The Court also noted that the writ of habeas corpus was a fundamental right that could not be denied by the federal government. In conclusion, the Supreme Court held that the state court had 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 fundamental right that could not be denied by the federal government. The Court also held that the state court had the authority to issue the writ, as long as the prisoner was held in the state.

Justice Field delivered the dissenting opinion in McCarthy v. Provost, arguing that the majority's decision was wrongfully decided and should be reversed. He argued that a contract between two parties is binding on both of them, regardless of any subsequent changes to state law or regulations. In this case, he noted that there had been an agreement between McCarthy and Provost for the sale of certain real estate which included a clause stating it would not become void if either party failed to comply with applicable laws or regulations. Therefore, Justice Field concluded that even though Provost did not obtain all necessary permits before selling the property as required by California law at the time, his failure could not invalidate their original contract since they had agreed otherwise in writing prior to its enactment.