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 South Carolina, a person or entity not originally part of a lawsuit may intervene in the case by filing a plea in intervention before the court renders a judgment. The process does not require the court's permission to intervene, but the intervention can be challenged by the opposing party through a motion to strike. The right to intervene is established if the potential intervenor has a significant interest in the lawsuit, such that they could have initiated the same lawsuit themselves or would have a defense against it if they were named as a defendant. The court may only strike an intervention if it fails to meet the criteria of having a substantial interest in the case, if it unduly complicates the issues, or if the intervention is not necessary to protect the intervenor's interests. If an intervenor satisfies the conditions for intervention and their participation does not excessively complicate the case, a trial court's decision to strike the intervention could be considered an abuse of discretion.