Third-Party Complaints (Impleader)

In explaining third-party complaints it's probably first best to understand the characters.  Imagine that X sues Y.  X would be the plaintiff, and Y the defendant. If Y then wants to bring Z into the lawsuit, Y would be known as a third-party plaintiff, and Z would be known as a third-party defendant.  And so the question becomes when is it allowable for Y to file a complaint against Z.

There's a specific rule that addresses this.  A defending party (Y) may serve a summons and complaint on a non-party ( Z) who is or may be liable to the defending party (Y) for all or part of the claim brought by the plaintiff (X) against the defending party (Y).  This is known as impleader, and it shows up with frequency on the MBE.

It's important to note the limitations of the impleader rule. It only applies if a third-party plaintiff is alleging that the third-party defendant is or may be liable to the third-party plaintiff for all or part of the claim originally brought against the third-party plaintiff. In other words, the third-party complaint must assert some sort of derivative liability. The third-party plaintiff cannot implead a third-party defendant if the reason for doing so is not for the reason stated above.

Put a bit more simply, a third-party claim may be asserted only when the third party defendant's liability is in some way dependent on the outcome of the main claim made by plaintiff against defendant or when the third party defendant is secondarily liable and not primarily liable to the original plaintiff.  So, if the third-party plaintiff wants to claim that the third-party defendant alone is liable to the original plaintiff, that would not be a proper basis for impleading the third-party defendant. That would be claiming direct liability, and the nature of third-party claims is derivative.