Direction From the Court on the Role of Expert Witnesses in Patent Cases

Expert evidence is essential in patent disputes. It provides specialized knowledge on the scientific and technical issues before the court – but the relationship between the expert witnesses and counsel is a delicate one. While the content of expert reports must be the expert’s independent and non-partisan opinion, counsel’s assistance is often required to ensure that expert reports are drafted in a way that effectively addresses the legal issue at hand.

The Federal Court of Appeal recently provided insight on the appropriate procedures for managing the relationship between expert witnesses and legal counsel in dTechs EPM v. British Columbia Hydro and Power Authority and Awesense Wireless Inc., 2023 FCA 115 (“dTechs EPM”).


dTechs, the patent owner, commenced an infringement action against Awesense and BC Hydro. The Federal Court determined that neither defendant had infringed the claims of the patent, and that the claims were invalid on the grounds of anticipation and obviousness. dTechs appealed the Federal Court’s decision solely on the basis that the evidence presented by BC Hydro’s expert witness should not have been considered. dTech alleged that the invoices for the expert’s services – obtained after trial – were evidence that they did not author their own reports and therefore did not qualify them as an independent or unbiased witness. dTech obtained the invoices when evaluating BC Hydro’s costs following the Federal Court’s decision. dTech brought this new evidence to the Federal Court of Appeal and premised their appeal on the allegation that the expert’s opinion was not independent.

At the Federal Court of Appeal, the court found that there was no evidence to support the proposition that the expert’s reports did not represent their objective and non-partisan opinion. Although the invoices did not include time entries related to the actual writing of the first drafts of the reports, the entries provided details that the expert read, reviewed and commented on the first drafts. The court inferred that the first draft of the report was written by BC Hydro’s counsel after discussions with the expert. The collaboration between BC Hydro’s counsel and the expert did not invalidate the expert’s evidence.

Importantly, the admissibility of the expert reports was not challenged at any time before the Federal Court’s decision was issued and was only raised as a ground of appeal after dTechs’ counsel had received the invoices. At the Federal Court of Appeal, Justice Gauthier determined that allowing parties to wait to review an expert’s invoices after the trial to argue that the invoices warrant a new trial would be contrary to the administration of justice.

The Federal Court of Appeal dismissed dTechs’ appeal and confirmed the Federal Court’s finding.

Appropriate Procedures for Providing Expert Evidence

In dTechs EPM, the Federal Court of Appeal provided important guidance on appropriate procedures for working with experts in patent cases. dTechs EPM is part of a chain of judicial decisions, including Moore v. Getahun (2015 ONCA 55) and Biogen Canada Inc. v. Pharmascience Inc. (2022 FCA 143), that addresses the collaboration between counsel and expert witnesses.

The following key guidance stems from working with expert witnesses in patent disputes:

  • Expert reports may be written in collaboration with counsel, so long as the report provides the court with the substantive and objective opinion of the expert. Collaboration can include having counsel draft the first version of the report following consultation with the expert.
  • Expert evidence can be invalidated if it does not reflect the objective and non-partisan opinion of the expert.
  • Concerns about the ability of an expert to provide independent, fair and objective advice should be raised as soon as possible. This can be before trial or during cross-examination.
  • If an expert is unwilling or unable to meet their duty to present independent and impartial evidence, the court will act as a gatekeeper to strike out their report.


Expert evidence is critical to almost all patent cases and lawyers must take steps to protect the independence and impartiality of the expert’s opinion.

Lawyers have a duty to ensure that their practices follow the ethical guidelines set out by the law society, just as many experts must follow the guidelines of their regulatory bodies. Specifically, in Federal Court, all parties are bound by the Federal Court Rules which provide a Code of Conduct for Expert Witnesses. By virtue of this code, experts must provide impartial evidence to the court and their duty to assist the court overrides any duty they may have to a party in the dispute. Above all, the code of conduct under the Federal Court Rules prioritizes the importance of independent, impartial and objective expert opinions.

If a lawyer suspects that these rules have been violated, they should bring it to the court’s attention as soon as possible. Lawyers ought to utilize the safeguards that are built into the adjudicative process by challenging biased expert opinions through cross-examination as soon as they suspect that the expert may be unwilling or unable to provide impartial evidence.

Aird & McBurney will continue to monitor procedures for managing the relationship between expert witnesses and legal counsel. Please contact one of the authors if you have questions or require assistance.