When litigation requires a technical expert
Judges decide cases. They are not engineers, chemists, or programmers. When a dispute turns on how something works, the court needs help understanding it.
The party that finds the right expert early often shapes how the judge comes to understand the technology.
What the law allows
Witnesses generally testify to facts, not opinions. Expert evidence is the exception. The Supreme Court of Canada's framework asks whether the evidence is relevant, necessary to assist the court, not excluded by another rule, and given by a properly qualified expert (R v Mohan, [1994] 2 SCR 9).
The expert must also be able and willing to give fair, objective, and non-partisan evidence. The judge then weighs the benefit of the evidence against its cost in time, expense and distraction (White Burgess Langille Inman v Abbott and Haliburton Co, 2015 SCC 23).
An expert's duty is to the court. In Ontario the expert signs an acknowledgment of that duty. As of September 1, 2026, the expert must also certify the accuracy of quotations in the report. The Federal Court has its own code of conduct for expert witnesses.
Cases that usually need one
Patents. Claims are read through the eyes of a person skilled in the relevant art (Whirlpool Corp v Camco Inc, 2000 SCC 67). Experts explain what that person would have understood.
Software and trade secrets. Whether code was copied or independently written is rarely apparent to a lay reader. The Supreme Court has accepted expert evidence where works need a perspective beyond the ordinary observer's (Cinar Corporation v Robinson, 2013 SCC 73).
Digital forensics. What was accessed, copied or deleted, and when.
Engineering and product disputes. Why something failed, or whether it met its specification.
Money. Lost profits, the defendant's profits, or a reasonable royalty.
Cases that may not
In trademark disputes over goods sold to the general public, the Supreme Court has cautioned that a judge can usually assess confusion without expert help, and that experts and surveys should be used with care (Masterpiece Inc v Alavida Lifestyles Inc, 2011 SCC 27).
Expert opinion on Canadian law is not admissible. That is the judge's job.
Numbers are limited too. A party who wants to call more than five experts in the Federal Court needs leave, and the court will weigh the expense against the amount in dispute. Ontario's limit is three without leave.
Two different roles
A consulting expert helps counsel understand the technology, test theories, and prepare cross-examination. They do not testify, and their work is generally protected by litigation privilege.
A testifying expert delivers a report and is cross-examined on it. Counsel may review drafts and discuss them with the expert, and those exchanges are generally protected unless there is reason to suspect improper influence (Moore v Getahun, 2015 ONCA 55). The final report must still disclose the expert's instructions and the facts and assumptions relied on.
In a case that turns on the technology, it can be worth having both.
Retain early
Pleadings. How the technology is described in the claim constrains everything after.
Injunctions. Technical points need affidavit evidence within days.
Discovery. An expert knows which documents and data to ask for.
Assessment. A candid expert delivers bad news when it is still cheap to hear.
Choosing well
Expertise in the specific field, at the time that matters to the case.
Independence. A connection to a party does not automatically disqualify an expert, but it invites attack.
The ability to teach. The best expert is the one the judge understands.
A consistent record. Prior testimony and publications will be read by the other side.
The Federal Court can order experts to confer before trial to narrow their differences, and can have them testify together as a panel. Expect your expert's opinion to be tested directly against the other side's.
An expert who argues the client's case loses the court's trust, and credibility is the reason for calling one.
This post is general information about Canadian law. It is not legal advice about your situation.
