A person or entity who is not a party to a lawsuit generally may intervene in the lawsuit and become a party to it by filing a plea in intervention prior to the entry of the court’s judgment—provided the court does not reject (strike) the intervention. An intervenor is not required to secure the court’s permission to intervene, and the party who opposed the intervention has the burden to challenge it by filing a motion to strike.

A person or entity has a right to intervene if the intervenor could have brought the same lawsuit, or any part of it in his own name—or, if the action had been brought against him, he would be able to defeat the lawsuit, or some part of it.

A trial court abuses its discretion by striking an intervention if (1) the intervenor meets the above test, (2) the intervention will not complicate the case by an excessive multiplication of the issues, and (3) the intervention is almost essential to effectively protect the intervenor’s interest.

In Illinois, the right to intervene in a lawsuit is governed by the Illinois Code of Civil Procedure. A non-party to a lawsuit may intervene by filing a petition to intervene before the court enters a judgment. The intervenor does not need to obtain permission from the court to intervene, but the intervention can be challenged by an existing party through a motion to strike. An entity or person has the right to intervene if they could have initiated the same lawsuit on their own, or if they would have a defense against the lawsuit if it were brought against them. The court may only strike an intervention if it fails to meet the criteria of the intervenor being able to bring or defend against the lawsuit, the intervention does not excessively complicate the case, and the intervention is necessary to protect the intervenor’s interests. If these conditions are met and the court still strikes the intervention, it may be considered an abuse of discretion.