Pickersgill v. Lahens 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 who was being held in a federal prison. The case arose when a prisoner, Pickersgill, was held in a federal prison in Maryland. Pickersgill sought a writ of habeas corpus from the state court in Maryland, but the state court refused to issue the writ. Pickersgill then appealed 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 state court should not be allowed to interfere with the federal government's power to protect this right. In conclusion, 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 state court should not be allowed to interfere with the federal government's power to protect this right.

In Pickersgill v. Lahens, the Supreme Court was tasked with determining whether a judgment of foreclosure and sale issued by a court in Louisiana against certain mortgaged property should be set aside due to irregularities in the proceedings leading up to it. The majority opinion held that the judgment should not be set aside since there were no errors or frauds committed during its issuance. However, Justice Field dissented from this ruling on two grounds: firstly, he argued that under Louisiana law at the time, any irregularity in procedure could invalidate such judgments; secondly, he noted that even if this weren't true according to state law, federal courts had an obligation to ensure fairness and justice when deciding cases involving mortgages over real estate located within their jurisdiction. Therefore Justice Field concluded that despite no evidence of error or fraud being present here, setting aside the judgment would still have been appropriate given these factors.