How to File a Complaint in Intervention in California

To file a complaint in intervention in California, you file a noticed motion under Code of Civil Procedure section 387 asking the court for permission to join an existing lawsuit, attach your proposed complaint as an exhibit, serve every party that has appeared, and then file the complaint itself only after the court grants leave.¹ You cannot drop your complaint on the clerk and walk into the case. A court order comes first.

What You Have to Show to Be Let In

Your motion has to argue one of two theories, and picking the right one shapes the whole package.

Intervention of right. The court must grant your motion if it is timely and either a California statute gives you an unconditional right to intervene, or you claim an interest in the property or transaction at the center of the case and the outcome could impair your ability to protect that interest. One carve-out: if an existing party already adequately represents your interest, the court can still deny you.¹

Permissive intervention. If you do not qualify as of right, the court can still let you in when you have an interest in the dispute, in the success of either side, or a claim adverse to both.¹ California courts weigh four things: whether you followed proper procedure, whether your interest is direct and immediate, whether your involvement will enlarge the issues, and whether the reasons to let you in outweigh the opposition. That last factor is where most permissive motions are won or lost. If existing parties can convince the judge that you will slow the case or complicate settlement, the answer is often no.

Section 387 lets you join on the plaintiff’s side, align with the defendant, or take a position adverse to both. You can file a complaint in intervention to assert affirmative claims, an answer in intervention to raise defenses, or both.

Drafting the Proposed Complaint in Intervention

Treat this pleading as the equivalent of the original plaintiff’s complaint, written from your perspective. It follows the same Superior Court formatting rules as any civil complaint.

The complaint should clearly identify the existing parties, state your position in the case, and explain why you belong there. Lay out the facts, state your legal theories, and describe the relief you want. Include a dedicated section tying your interest to the requirements of section 387, since the judge reads this pleading before deciding whether to grant leave. A vague or sloppy proposed complaint signals that your intervention will create more problems than it solves, and that alone can sink the motion.

The Motion Package

The statute requires a noticed motion, or in genuinely urgent circumstances an ex parte application.¹ A complete package includes:

Notice of Motion stating what you are asking for, when the hearing is set, and in which department.
Memorandum of Points and Authorities working through the statutory requirements and showing, point by point, how your situation meets them. This is the document that decides the motion.
The proposed Complaint in Intervention attached as an exhibit so the court and opposing parties can see the claims.
A supporting declaration giving the factual background: when and how you learned of the lawsuit, what your interest is, and why the existing parties do not adequately represent it.

Filing Fees

A complaint in intervention counts as a first paper filing in the case for fee purposes. In an unlimited civil case (amount in controversy over $25,000), the filing fee is $435. Limited civil cases run $225 to $370 depending on the amount at stake.² Riverside, San Bernardino, and San Francisco counties may add a courthouse construction surcharge. Fee waivers are available if you cannot afford the fee.

Serving the Motion

Every party that has appeared in the case must be served with the moving papers. Miss one, and the motion can be derailed.

Under Code of Civil Procedure section 1005, a noticed motion must be served at least 16 court days before the hearing. Add five calendar days for service by mail within California, or two calendar days for overnight delivery. These are the standard noticed-motion deadlines and they apply here.

File Early: The Timeliness Problem

Both categories of intervention require a timely application, and there is no fixed deadline in the statute. Courts decide timeliness on the facts of each case, and this is where many motions fail.

The rule California courts apply is that an intervener “must not be guilty of an unreasonable delay after knowledge of the suit.” Waiting several years and then moving to intervene after the existing parties have negotiated a comprehensive settlement is a near-certain denial, because last-minute intervention prejudices parties who have already resolved their dispute. Courts have, by contrast, found intervention timely when the applicant moved immediately after learning that damages were being sought. File as soon as you know your interests are at stake. Every week of delay becomes ammunition for the opposition.

After the Court Grants Leave

A granted motion is not the end of the paperwork. You then separately file the complaint in intervention with the court and serve it on all existing parties along with a copy of the order granting your motion.¹

Service rules depend on whether the party you are serving has already appeared:

Parties who have not appeared must be served using formal summons methods, such as personal delivery or substituted service under CCP section 415.10 and following.
Parties who have appeared can be served the same way, or through the standard methods for serving papers on parties already in the case (mail, authorized electronic service, or personal delivery to counsel).¹

Once served, existing parties have 30 days to respond with an answer, a demurrer, or another challenge to your pleading, just as they would to any original complaint.¹ From that point you are a full party, with the same discovery rights, motion rights, and obligations as the original litigants.

If the Motion Is Denied

A denied motion to intervene is generally appealable in California, because the denial ends the proceeding for the person who tried to intervene. Appellate deadlines are strict and typically run 60 days from the order, so consult an attorney promptly about a notice of appeal.

Federal Court Cases Use a Different Rule

If the underlying lawsuit is in a federal district court in California rather than a state Superior Court, intervention is governed by Federal Rule of Civil Procedure 24, not CCP section 387.³ The structure is similar, but federal filing fees, procedural requirements, and the explicit instruction to weigh delay and prejudice to the original parties all differ. Check the case caption: a Superior Court case names the county, while a federal case names the United States District Court for a particular district of California.

1
California Legislative Information. California Code of Civil Procedure Section 387 – Intervention
2
California Courts. Superior Court of California Statewide Civil Fee Schedule
3
Legal Information Institute. Federal Rules of Civil Procedure Rule 24 – Intervention