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 Maryland, the rules for intervention in a lawsuit are governed by the Maryland Rules of Civil Procedure. A person or entity, known as an intervenor, may seek to become a party to an existing lawsuit by filing a motion to intervene. The right to intervene is typically granted if the intervenor has an interest that is directly affected by the outcome of the case. The intervenor must demonstrate that they could have initiated the same lawsuit or have a defense to the action if it were brought against them. The court has the discretion to allow or deny the intervention, but it may be considered an abuse of discretion if the intervenor meets the criteria of having a significant interest in the case, the intervention does not overly complicate the issues, and the intervention is necessary to protect the intervenor's interests. The burden to challenge an intervention lies with the party opposing it, who must file a motion to strike the intervention. It is important to note that while the general right to intervene exists, the specific circumstances and timing of the intervention can affect the court's decision.