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 Florida, the rules regarding intervention in a lawsuit are governed by the Florida Rules of Civil Procedure. Specifically, Rule 1.230 allows a person or entity to intervene in a pending 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, unless their interest is adequately represented by existing parties. The intervenor is not required to obtain permission from the court to intervene, but they must file a motion and serve a copy to all parties. The burden to challenge the intervention lies with the party opposing it, who must file a motion to strike the intervention. The court may strike an intervention if it does not meet the criteria set forth, such as if the intervenor could not have brought the lawsuit themselves or if the intervention would unduly complicate the case or is not necessary 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 necessary criteria, does not excessively complicate the case, and is nearly essential to protect the intervenor's interests.