In Pratt v. Fitzhugh et al., the Supreme Court of the United States held that a slave named John, who had been taken from Virginia to Maryland and then back to Virginia by his owner, was not entitled to freedom under the laws of either state. The court reasoned that since slavery is recognized as valid in both states, it would be inconsistent with their respective public policies for one state's law to free a slave belonging to another state. Furthermore, even if John could have claimed freedom under Maryland law due to his temporary residence there, he did not do so within a reasonable time after returning from Maryland and thus forfeited any such claim. As such, the court affirmed the judgment of lower courts denying John's petition for freedom on this basis.

In Pratt v. Fitzhugh et al., the Supreme Court was asked to decide whether a slave named Henry, who had been taken by his owner from Virginia to Pennsylvania and then back again, could be considered free under the laws of Pennsylvania. The majority opinion held that since slavery is not recognized in Pennsylvania, Henry should remain enslaved despite having traveled there with his master. However, Justice Grier dissented from this decision on two grounds: firstly, he argued that when a person enters another state they are subject to its laws; secondly he noted that if any other form of property were brought into a state it would be protected by local law regardless of where it originated from or what the laws governing it may have been elsewhere. Therefore Grier concluded that Henry should be considered free while in Pennsylvania as per their anti-slavery statutes and thus must remain so upon returning home even though Virginia did recognize slavery at the time.