Rule 24.Intervention
Part IV. Parties · Last verified September 4, 2026
Full Text of Rule 24
Plain-English Summary
Rule 24 is identical to its civil counterpart, and the source says so in a line of its own before subsection (a).
Intervention of right
On timely application, a person shall be permitted to intervene when a statute of the Commonwealth confers an unconditional right, or when the applicant claims an interest relating to the property or transaction that is the subject of the action and is so situated that disposition of the action may as a practical matter impair or impede their ability to protect that interest — unless the interest is adequately represented by existing parties.
The adequacy proviso is where most of these applications are decided. In a domestic relations case the familiar candidates are a grandparent or other relative with a claim relating to a child, a third party with an interest in property being divided, or a public agency.
Permissive intervention
Subsection (b) allows intervention where a statute confers a conditional right, or where the applicant's claim or defense and the main action share a common question of law or fact. A government officer or agency may intervene where a party relies for a claim or defense on a statute, executive order, regulation, requirement or agreement that officer or agency administers. In exercising its discretion the court considers whether the intervention will unduly delay or prejudice the adjudication of the rights of the original parties.
Procedure, and the Attorney General
Subsection (c) requires a motion to intervene served on the parties under Rule 5, stating the grounds and accompanied by a pleading setting forth the claim or defense for which intervention is sought. The pleading is not optional.
Subsection (d) requires notice to the Attorney General where the constitutionality of an act of the legislature, or the constitutionality or validity of a city ordinance or town by-law, is drawn in question in an action to which the Commonwealth or its officer, agency or employee is not a party. The duty falls on the party asserting the invalidity, and the notice must come in sufficient time to afford an opportunity to intervene.
Frequently Asked Questions
When can someone intervene as of right?
Under Rule 24(a), on timely application, where a statute of the Commonwealth confers an unconditional right to intervene, or where the applicant claims an interest relating to the property or transaction that is the subject of the action and is so situated that disposition of the action may as a practical matter impair or impede their ability to protect that interest — unless that interest is adequately represented by the existing parties.
What has to accompany a motion to intervene?
Rule 24(c) requires the motion to state the grounds and to be accompanied by a pleading setting forth the claim or defense for which intervention is sought. The motion is served on the parties as provided in Rule 5.
What does the court weigh on permissive intervention?
Rule 24(b) directs the court, in exercising its discretion, to consider whether the intervention will unduly delay or prejudice the adjudication of the rights of the original parties.
When does the Attorney General have to be notified?
Under Rule 24(d), when the constitutionality of an act of the legislature, or the constitutionality or validity of a city ordinance or town by-law, is drawn in question in an action to which the Commonwealth or an officer, agency or employee is not a party. The party asserting invalidity must give notice in sufficient time to afford an opportunity to intervene.