Marshall v. Hubbard was a United States Supreme Court case that addressed the issue of whether a state court could issue a writ of habeas corpus to a prisoner who was being held in federal custody. The case arose when the petitioner, Marshall, was arrested and charged with a federal crime. He was then held in federal custody pending trial. Marshall then filed a petition for a writ of habeas corpus in a state court, arguing that he was being unlawfully detained. The state court granted the writ and ordered Marshall to be released. The federal government then appealed the decision to the Supreme Court, 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 agreed with the federal government, holding 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 prerogative and that the state court did not have the authority to interfere with the federal government's power to detain a prisoner. The decision in Marshall v. Hubbard established that state courts do not have the authority to issue a writ of habeas corpus to a prisoner in federal custody. This decision has been cited in numerous subsequent cases and has become an important precedent in the area of federal-state relations.

Justice Field delivered the dissenting opinion in Marshall v. Hubbard, arguing that the majority's decision was contrary to both law and equity. He argued that a contract between two parties should be enforced according to its terms unless there is some legal or equitable reason why it should not be enforced. In this case, he argued that no such reasons existed; therefore, the contract should have been enforced as written. Furthermore, Justice Field noted that while courts may modify contracts when necessary for justice and fairness, they cannot do so if doing so would alter the meaning of an unambiguous agreement or impose obligations on one party which were not agreed upon by both parties at the time of signing. As such, he concluded that since neither party had requested any modifications prior to entering into their agreement nor did either party seek relief from any court before filing suit against each other over breach of contract claims - then their original agreement must stand as-is and be fully enforceable in accordance with its plain language without modification by a court of law.