Sheehy v. Mandeville was a case heard by the United States Supreme Court in 1812. The dispute arose when Sheehy, an Irish immigrant, purchased land from Mandeville and then attempted to secure title to it through a process known as “quieting of title” which involved proving ownership before a court of law. However, due to his status as an alien at the time he could not do so under existing laws that prohibited aliens from owning property in certain states. As such, Sheehy brought suit against Mandeville claiming that he had been fraudulently induced into purchasing the land without being informed about this restriction on his ability to obtain legal title for it. In its decision, the Supreme Court held that while aliens were indeed barred from obtaining legal titles for lands they owned in certain states they still had rights with respect to their possession and use of those lands until such time as they chose or were able to transfer them legally; thus affirming Sheehy's right over his property despite not having obtained formal legal recognition of it yet.

In Sheehy v. Mandeville, Chief Justice Marshall delivered the dissenting opinion of the Supreme Court. He argued that a contract between two parties should be enforced even if it was made in violation of an existing law or statute. According to him, when two individuals enter into a valid agreement and one party has already performed their part of the bargain, then they are entitled to receive compensation for their services regardless of any laws that may have been broken in order to make such an agreement possible. The majority's decision would leave both parties without recourse since neither could enforce their rights under the contract due to its illegality; thus, he believed this result was unjust and contrary to established principles of equity and justice.