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 North Carolina, the rules for intervention in a lawsuit are governed by the North Carolina Rules of Civil Procedure, specifically Rule 24. A person or entity may intervene in an ongoing lawsuit if they have an interest that is significantly protectable and related to the property or transaction that is the subject of the action. The intervenor must demonstrate that their ability to protect their interest may be impaired if they do not intervene, and that their interest is not adequately represented by the existing parties. Intervention can be as of right or permissive. As of right intervention is allowed when the intervenor claims an interest relating to the property or transaction which is the subject of the action, and they are so situated that disposing of the action may as a practical matter impair or impede their ability to protect that interest. Permissive intervention is at the discretion of the court and may be granted when an applicant's claim or defense and the main action have a question of law or fact in common. The party opposing the intervention has the burden to challenge it by filing a motion to strike. A trial court may be found to have abused its discretion if it strikes an intervention that meets the criteria of having a significant interest in the lawsuit, not complicating the case excessively, and being essential to protect the intervenor’s interests.