In what scenario will a third-party defendant be relevant to the jurisdiction of a case?

The relevance of a third-party defendant to the jurisdiction of a case mainly pertains to how that party interacts with the established jurisdiction, particularly when considering the diversity of citizenship and the supplemental jurisdiction.

When a third-party defendant is a citizen from the same state as the original plaintiff, this scenario can affect the court's diversity jurisdiction. In cases where there is no complete diversity—meaning that the plaintiff and the defendant (and any third-party defendants) are from the same state—federal courts will not have subject matter jurisdiction based on diversity. If a third-party defendant shares citizenship with the original plaintiff, it can destroy the complete diversity required for federal jurisdiction.

For this reason, the presence of a third-party defendant from the same state as the original plaintiff is particularly relevant; it provides insight into whether diversity jurisdiction is maintained or destroyed. Thus, the scenario where the third-party defendant is a citizen from the same state as the original plaintiff is integral to the determination of whether the federal court can continue to exercise jurisdiction over the case.

In contrast, claims brought by the original plaintiff do not directly pertain to the jurisdictional analysis of the third-party defendant. The establishment of diversity prior to the inclusion of additional parties and the requirement for additional jurisdictional facts do not