How Patent Infringement Suits Work in Delhi High Court

What a patent infringement suit is, and who files one

A patent gives its owner the exclusive right, for 20 years from the filing date, to stop others from making, using, offering for sale, selling or importing the patented product in India, or from using the patented process and dealing in products made by it (Section 48 of the Patents Act 1970). A patent infringement suit is how that right is enforced. The patentee, or an exclusive licensee in the cases the Act allows, files a civil suit asking for an injunction, damages or an account of profits, and delivery up or destruction of infringing goods (Section 108).

The suit can only be filed after grant. An applicant whose application has been published gets rights from the date of publication, so damages may later reach back to that date, but proceedings cannot start until the patent is actually granted (Section 11A(7)). Patentees sometimes miss this and send threat letters on a pending application, which can expose them to a claim for groundless threats under Section 106.

Most patent suits in the Delhi High Court involve pharmaceuticals, agrochemicals, mobile phones and telecom standards, medical devices, and industrial machinery. The parties are usually companies, but small manufacturers in Okhla, Bawana or Noida are often on one side or the other, either as an alleged infringer supplying a component or as a local patentee whose design has been copied.

A patent case is costlier and slower than a trademark case. The court must understand the technology, interpret the claims, and often decide whether the patent was valid in the first place. That is why the preparation before filing, or before replying, matters more here than in most civil disputes.

Before you sue: test the patent and the evidence

Start with the patent itself. Pull the granted claims from the Patent Office record, not the published application, because claims are often narrowed during examination. Read the file history: objections raised by the examiner, amendments made, oppositions filed, and arguments the applicant gave to get the patent granted. A patentee who told the Patent Office that the invention did not cover a particular feature cannot later argue that a rival with that feature infringes.

Next, build the claim chart. Each independent claim is split into its elements, and each element is matched with evidence from the accused product or process: a test report, a teardown, a laboratory analysis, product literature or a regulatory filing. If even one element is missing in the accused product, there is no literal infringement, and an argument of equivalence will have to carry the case.

Collect proof of sale. Test purchases with invoices, online orders delivered in Delhi, distributor catalogues and tender documents show who is selling, where and since when. They also support the court's jurisdiction. Keep the purchased products sealed with the invoice and a note of who bought them and when.

Finally, run your own validity check. If the defendant can show prior art that discloses the invention, the patent may be revoked and the suit will fail. Patentees who skip this step get surprised at the first hearing. Check also that renewal fees are paid and that the working statements in Form 27 have been filed, since gaps in either will be raised against you.

Which court hears a patent suit, and why so many are in Delhi

Section 104 of the Patents Act says an infringement suit cannot be filed in any court below a District Court. In Delhi, a patent suit valued above the High Court's pecuniary limit (Rs 2 crore at present; a proposal to raise it is pending, so check the current limit) is filed on the original side of the High Court as a commercial suit. A lower-valued suit goes to the District Judge (Commercial) with territorial jurisdiction. But the proviso to Section 104 changes the picture: once the defendant files a counter-claim for revocation, the whole suit is transferred to the High Court.

Inside the High Court, patent suits are listed before the Intellectual Property Division, set up after the Intellectual Property Appellate Board was abolished in 2021 and governed by the IPD Rules 2022. The court also notified the High Court of Delhi Rules Governing Patent Suits in February 2022. Our guide on the Intellectual Property Division of the Delhi High Court explains how that division is organised, and our guide on which commercial cases go to the Commercial Division explains valuation.

Territorial jurisdiction follows Section 20 of the Code of Civil Procedure: where the defendant resides or carries on business, or where the cause of action arose in whole or part. Unlike the Trade Marks Act and the Copyright Act, the Patents Act has no special provision letting the patentee sue where it carries on business. So a Delhi suit usually rests on sales, offers for sale or supply in Delhi. For online sales, the Division Bench test in Banyan Tree Holding v. A. Murali Krishna Reddy (2009) requires more than a website that can be viewed in Delhi; the seller must have targeted Delhi customers, and evidence of an actual sale here helps.

Patentees prefer Delhi because the IP Division has settled practices for technical cases, a panel of scientific advisers, and judges who hear a steady flow of patent matters. Defendants who have no real presence in Delhi should check whether the plaint actually shows a cause of action here; a jurisdiction objection, raised early, can be decisive.

The provisions that shape a patent case

How a patent infringement suit moves in the Delhi High Court

1. Pre-filing work

   Claim chart, test purchases, validity check, and a decision on whether to send a notice first. A notice can lead to settlement, but it also warns the defendant to file a revocation petition or a suit for declaration in its own chosen forum.

2. Filing the plaint

   The plaint is e-filed with the patent, file history, claim chart, evidence of infringement and sale, a statement of truth, and an application for interim injunction. Where urgent relief is sought, mediation under Section 12A is not required. The Patent Suit Rules require specific details in the plaint, including the patent's status, related proceedings and licensing history.

3. First hearing

   The court may grant an ex parte interim order if the case is strong and delay would cause serious harm, issue summons and notice, appoint a local commissioner to inspect or seize goods, or ask the defendant to keep accounts of sales. More often in patent cases, the court issues notice and lists the interim application for hearing with both sides present.

4. Written statement and counter-claim

   The defendant files its written statement within 30 days, extendable to a maximum of 120 days from service, with any counter-claim for revocation. The plaintiff replies with a replication and a written statement to the counter-claim.

5. Interim injunction hearing

   Both sides argue the interim application on affidavits, technical documents and expert declarations. This hearing can run over several dates. The order decides whether the defendant must stop pending trial, deposit money, or keep accounts.

6. Case management hearings

   Under the Patent Suit Rules, the court holds case management hearings, may direct a joint technical primer explaining the science, fixes the schedule for claim construction briefs, decides on a confidentiality club for sensitive documents, and frames issues.

7. Evidence and experts

   Witnesses give evidence by affidavit and are cross-examined, often before a local commissioner. Expert evidence may be recorded by hot-tubbing, where experts from both sides are examined together. The court may take help from a scientific adviser under Section 115.

8. Final hearing and judgment

   Arguments on infringement, validity and damages, followed by judgment. Damages may be assessed in the judgment or in a separate inquiry.

The interim patent injunction hearing

The interim hearing is where most patent suits are won or lost. The court asks the usual three questions (a prima facie case, the balance of convenience, and irreparable harm), but in patent cases the first question has two parts: does the product fall within the claims, and has the defendant raised a credible challenge to the patent's validity? The defendant does not have to prove invalidity at this stage. It needs to show a serious, substantial challenge, not a speculative one. If it does, a patent injunction is usually refused, sometimes on terms such as keeping accounts or depositing a share of sales.

Public interest weighs heavily in pharmaceutical cases. In F. Hoffmann-La Roche v. Cipla (2008 and 2009), the Delhi High Court declined an interim injunction against a cheaper version of a cancer drug, partly because of the effect on patients. In Merck Sharp and Dohme v. Glenmark (2015), a Division Bench granted one where the validity challenge was weak. The court looks at the facts of each patent, the price difference, and how long the patent has stood without a successful challenge.

A patentee who waits too long weakens its case for urgent relief. If the defendant has been selling openly for two years, the court will ask why the plaintiff now says it cannot wait for trial. Equally, a defendant who launches after receiving a clear warning, without a written opinion on non-infringement or invalidity, takes a risk that the court will see as deliberate.

Quia timet suits are common in Delhi. A patentee who learns that a generic maker has obtained regulatory approval and plans to launch can sue before any sale, asking the court to stop the launch. The defendant then has to show its case quickly, often within weeks. For more on orders passed without the other side, see our guide on ex parte injunctions in IP cases.

The defendant's side: revocation counter claim and other defences

A defendant served with a patent suit has three lines of defence, and usually runs all three. First, non-infringement: the accused product lacks one or more elements of the claims, or works in a different way. Second, invalidity: the patent should not have been granted because the invention was known or obvious, was insufficiently described, or falls under an exclusion in Section 3, such as Section 3(d) for new forms of known substances without enhanced efficacy, applied by the Supreme Court in Novartis v. Union of India (2013). Third, specific statutory defences, such as the Bolar exemption or a licence.

A revocation counter claim is filed with the written statement and is treated as a cross-suit. It must set out each ground with the prior art relied on. Prior art searches take time, especially for older technologies documented in foreign-language publications or old product catalogues, and they cannot wait until day 110 of the 120-day window.

When Advocate B.K. Singh receives a patent suit for a defendant, the first two things he puts on the file are the date of service, with the 120-day outer limit worked out, and the name of the technical person who will run the prior art search. The Supreme Court held in SCG Contracts v. K.S. Chamankar Infrastructure (2019) that the 120-day limit in commercial suits is mandatory, so a written statement filed late is simply not taken on record.

A defendant can also act before being sued. If a rival has sent threat letters to its customers, a suit for groundless threats or a declaration of non-infringement may be filed. Any person interested can file a revocation petition directly in the High Court under Section 64, or a post-grant opposition before the Patent Office within one year of the grant being published. Choosing between these needs care, because each runs on different evidence rules and timelines.

Pharma, telecom and technology cases: what differs

Pharmaceutical suits move fast at the start because launch dates and regulatory approvals drive them. The questions are often about Section 3(d), about whether a later patent on a salt or crystal form adds anything to an earlier compound patent, and about whether the generic falls within the claims as granted. Evidence comes from regulatory dossiers, laboratory analysis and the patentee's own earlier filings.

Standard essential patent cases, mostly about mobile phones, are a different kind of dispute. The patentee has promised to license on fair, reasonable and non-discriminatory (FRAND) terms, and the real fight is over royalty. Since 2023, Division Benches of the Delhi High Court have directed some implementers to deposit pro-tem security pending trial, based on past licences or the royalty the implementer has offered. Judgments after trial in such cases have awarded large damages. An importer or assembler of devices should look at its licensing position before a suit, not after.

Mechanical and engineering cases, such as machine parts, filters or construction products, often turn on simple claim construction and on prior art from catalogues, trade fairs and earlier Indian patents. These suits are sometimes valued below the High Court's limit and begin in the district commercial court, then move to the High Court when a counter-claim is filed.

Time and cost at each stage (typical ranges, not promises)

Documents to collect

Evidence, experts and confidentiality clubs

Patent cases are won on technical evidence presented clearly. The court is not looking for the most qualified expert in the country; it wants someone who understands the field as an ordinary skilled person would, and who can explain the claims and the prior art without overstatement. An expert who concedes obvious points gains credibility. One who argues every point like an advocate loses it.

Sensitive documents, such as manufacturing processes, royalty rates and licence terms, are often shown only to a confidentiality club of named lawyers and experts, under the Patent Suit Rules. Each side should decide early who will be in the club, because a company's own technical staff may or may not be admitted, depending on the court's order.

On the plaintiff's side, Advocate B.K. Singh's practical advice is to have the claim chart checked by an independent technical person before filing, not just by the in-house team that worked on the invention. Inventors tend to read their claims broadly. A judge reads them as written, and a chart that stretches a claim to fit the accused product is usually the first thing the defendant attacks.

Damages, account of profits and costs

A successful patentee chooses between damages and an account of the defendant's profits. Damages are based on the patentee's lost sales or a reasonable royalty; an account of profits takes what the defendant earned from the infringement. Either needs evidence: sales figures, margins, licence rates for comparable technology. The court can order the defendant to disclose its sales, and the interim order often requires it to file accounts periodically.

Costs in commercial suits follow the event under Section 35 of the Code of Civil Procedure as substituted by the Commercial Courts Act, so the losing side generally pays the winner's reasonable costs. The court considers the parties' conduct, including frivolous claims, refusal to settle reasonably, and delay. A patentee who loses because its patent is revoked can face a significant costs order.

Limitation for damages is generally three years from each act of infringement, and an ongoing infringement gives a fresh cause of action while it continues. Delay does not always bar the suit, but it can reduce damages and weaken the case for an injunction.

Appeals and parallel proceedings

An order granting or refusing an interim injunction can be appealed to a Division Bench of the Delhi High Court under Section 13 of the Commercial Courts Act read with Order 43 of the Code of Civil Procedure, within 60 days. Appeals against interim orders are argued on the record before the single judge, so the affidavits and documents filed at the interim stage need to be complete. Our guide on commercial appeals under Section 13 covers the procedure.

Parallel proceedings are common. A post-grant opposition may be pending before the Patent Office, a revocation petition may be pending in the High Court, and an appeal against the Controller's order on the opposition may follow under Section 117A. Appeals from the Patent Office now lie to the High Court, as explained on our page on appeals against Trademark Registry and Patent Office orders. The court often hears related matters together to avoid conflicting results.

After the Division Bench, the remaining route is a special leave petition to the Supreme Court, which interferes in interim patent orders only rarely. Most parties settle at some point after the interim order, on a licence, a design change or a payment.

Mistakes that hurt patent cases

• Suing on the published claims. Claims change during examination; the suit must be based on the claims as granted.
• A claim chart that stretches the claims. If one element is missing from the accused product, an overreaching chart damages the patentee's credibility.
• Starting the prior art search late. The 120-day limit for the written statement does not move, and the counter-claim needs the search results.
• Long delay before suing. Years of silence after knowing of the infringement weaken the urgency argument for an interim injunction.
• Threat letters to customers without care. Sending wide warnings to a rival's customers can invite a groundless threats claim under Section 106.
• Ignoring jurisdiction. A Delhi suit needs a real cause of action in Delhi; a website visible here is not enough by itself.
• No sales records. A defendant that cannot show its own sales figures struggles when the court asks for accounts or a deposit.

What to do this week

If you are the patentee, get the granted claims and the file history, confirm renewals and Form 27 filings, and start a claim chart with a technical person who did not work on the invention. Make a test purchase in Delhi with an invoice. Decide whether a notice helps or simply warns the rival to file first.

If you have been served, write down the date of service and the 120-day outer limit, collect the product's design and development records with dates, and start a prior art search. Do not change the product quietly without advice, because a sudden change can be read as an admission, though a documented design-around can also be a sound commercial step. Keep a record of sales from the date of the plaint.

Both sides should consider early whether a licence or settlement makes more sense than years of trial. The matching service page on patent and design disputes in the Delhi High Court sets out how these cases are handled, and how fees are discussed and agreed in writing at the first meeting.

Advice on a patent dispute

A patent infringement suit is decided by three things: how well the claims read on the accused product, how strong the validity challenge is, and whether the interim hearing is prepared properly on both sides. For more on how patent and design cases are run, see our page on patent and design suits, and for larger commercial suits generally, our page on commercial suits above Rs 2 crore.

For advice on your patent, the plaint served on you, or a threat letter, or for updates on the law and the Delhi High Court's patent practice, contact Advocate B.K. Singh.