McNitt v. Turner 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 a federal prison. The case arose when a prisoner, McNitt, was held in a federal prison in the state of Missouri. McNitt sought a writ of habeas corpus from the state court, which the court granted. The federal government then 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 a federal prison. 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 imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the federal government had the exclusive power to protect this right. The decision in McNitt v. Turner established that the federal government had exclusive authority over the writ of habeas corpus, and that state courts could not interfere with the federal government's power to imprison individuals. This decision has been cited in numerous subsequent cases, and has been used to support the idea that the federal government has exclusive authority over the writ of habeas corpus.

In the case of McNitt v. Turner, the Supreme Court was asked to decide whether a contract between two parties could be enforced when it had been made in violation of an existing state law. The majority opinion held that such contracts were not enforceable and should not be upheld by the court. However, Justice Field dissented from this decision and argued that while he agreed with the majority's conclusion that contracts made in violation of state laws are generally unenforceable, there may be cases where enforcing them is necessary for justice to prevail. He reasoned that if one party has already performed their part of a contract before learning about its illegality then they should still receive some form of compensation or restitution for their efforts even if it means disregarding a state law in order to do so. Ultimately, Justice Field concluded that although courts must always respect validly enacted laws they also have an obligation to ensure fairness whenever possible which can sometimes require setting aside those same laws when circumstances warrant it.