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 Nevada, the rules regarding intervention in a lawsuit are governed by the Nevada Rules of Civil Procedure (NRCP). According to NRCP 24, a person or entity may intervene in an ongoing lawsuit if they have an interest relating to the property or transaction that is the subject of the action. The intervenor must be so situated that disposing of the action may as a practical matter impair or impede their ability to protect their interest, unless existing parties adequately represent that interest. Intervention can be as of right or permissive. For an intervention as of right, the intervenor must claim an interest that might be impaired by the disposition of the case and that interest is not adequately represented by existing parties. For permissive intervention, the court has discretion to allow intervention if there is a common question of law or fact between the intervenor's claim or defense and the main action. The intervenor is not required to obtain permission to intervene, but the opposing party can challenge the intervention by filing a motion to strike. The court may strike the intervention if it fails to meet the necessary criteria, excessively complicates the case, or is not essential to protect the intervenor’s interests. A trial court may be found to have abused its discretion if it strikes an intervention that meets the criteria for intervention, does not unduly complicate the case, and is nearly essential to protect the intervenor's interests.