Lynch v. De Bernal 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, John Lynch, was arrested by federal authorities in Texas and held in federal custody. Lynch 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 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 Court also noted that the writ of habeas corpus was a fundamental right and that the federal government had the right to protect its citizens from unlawful detention. The Court's decision in Lynch v. De Bernal established that the federal government had the exclusive authority to issue writs of habeas corpus and that state courts could not interfere with the federal government's power to detain a prisoner. This decision has been cited in numerous subsequent cases and has been used to support the federal government's authority to detain prisoners.

In Lynch v. De Bernal, the Supreme Court was tasked with deciding whether a contract between two parties could be enforced when one of them had died before it was fully executed. The majority opinion held that the contract in question could not be enforced because it had not been completed by both parties prior to the death of one party. However, Justice Field dissented from this decision and argued that contracts should still be enforceable even if they are incomplete at the time of death as long as there is evidence that both parties intended to enter into an agreement and were making progress towards completing it. He reasoned that allowing such contracts would encourage people to enter into agreements knowing their rights will still be protected even if something happens during negotiations or execution which prevents completion prior to death.