Enacted effective October 1, 2011 · Last verified June 26, 2026
In one sentenceRule 24 lets a non-party join an existing lawsuit — as of right when a statute allows or the person’s interest could be impaired and is not adequately represented, or permissively when there is a common question of law or fact.
(a)Intervention of Right. On timely motion, the court must permit anyone to intervene who:
(1)is given an unconditional right to intervene by statute; or
(2)claims an interest relating to the property or transaction which is the subject of the action, and is so situated that disposing of the action may as a practical matter impair or impede the movant’s ability to protect its interest, unless the existing parties adequately represent that interest.
(1)In General. On timely motion, the court may permit anyone to intervene who:
(A)is given a conditional right to intervene by statute; or
(B)has a claim or defense that shares with the main action a common question of law or fact.
(2)By a Government Officer or Agency. On timely motion, the court may permit a state governmental officer or agency to intervene if a party’s claim or defense is based on:
(A)a statute or executive order administered by the officer or agency; or
(B)any regulation, order, requirement, or agreement issued or made under the statute or executive order.
(3)Delay or Prejudice. In exercising its discretion, the court must consider whether the intervention will unduly delay or prejudice the adjudication of the original parties’ rights.
(c)Notice and Pleading Required. A motion to intervene must be served on the parties as provided in Rule 5. The motion must state the grounds for intervention and be accompanied by a pleading that sets out the claim or defense for which intervention is sought.
Plain-English Summary
Sometimes a lawsuit will affect someone who isn't a party. Rule 24 lets that person ask to join.
Intervention of right (subdivision (a)) must be allowed when a statute gives an unconditional right to intervene, or when the movant claims an interest in the property or transaction at issue that the case may, as a practical matter, impair — unless the existing parties already adequately represent that interest. Permissive intervention (subdivision (b)) is discretionary: it is available when a statute gives a conditional right, or when the movant's claim or defense shares a common question of law or fact with the main action; a government officer or agency may also intervene over statutes or regulations it administers. In exercising its discretion the court weighs whether intervention would unduly delay or prejudice the original parties. A motion to intervene must be served under Rule 5 and accompanied by a pleading stating the claim or defense.
Frequently Asked Questions
What is intervention?
It is when someone who is not already a party joins an existing lawsuit to protect their own interest in the outcome.
What is the difference between intervention of right and permissive intervention?
Intervention of right must be allowed (a statute grants it, or the person's interest could be practically impaired and is not adequately represented). Permissive intervention is discretionary and available when the person's claim or defense shares a common question of law or fact with the case.
Source & verification. Reproduced verbatim from the Montana Code Annotated as
published by the State Law Library of Montana and the Montana Legislature. This rule has not been amended since its adoption.
Adopted by the Supreme Court of Montana (AF 07-0157). Last verified June 26, 2026. ·
Official text
Also known as:interventionintervenemotion to interveneintervention of right