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 Minnesota, the rules regarding intervention in a lawsuit are governed by both state statutes and the Minnesota Rules of Civil Procedure. Under Rule 24 of the Minnesota Rules of Civil Procedure, a person or entity may intervene in a lawsuit if they have an interest relating to the property or transaction that 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. Intervention can be as of right or permissive. A party has the right to intervene when, among other situations, the party could have initiated the same lawsuit or if the lawsuit had been brought against them, they could defend against it. Permissive intervention is allowed by the court's discretion, typically when the intervenor has a claim or defense that shares a common question of law or fact with the main action. The court must consider whether the intervention will unduly delay or prejudice the adjudication of the original parties' rights. If an intervention is improperly struck down by the trial court, it may be considered an abuse of discretion if the intervenor meets the criteria for intervention, the intervention does not excessively complicate the case, and the intervention is necessary to protect the intervenor’s interests. The burden to challenge an intervention lies with the party opposing it, typically by filing a motion to strike.