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Expert Witness Report:

A Well Documented and Supported Opinion from a Subject Matter Expert



Last Updated: July 03 2026

Question: How can a Ontario paralegal or litigation support team help me prepare an expert witness report that will be admissible for civil court in Ontario?

Answer: A properly prepared expert witness report supports admissibility by meeting the R. v. Mohan, 1994 CanLII 80 (SCC), 1994 SCC 80 criteria for relevance and necessity, and by ensuring the expert is qualified and the report does not fall afoul of exclusionary rules, then having the judge balance potential risks and benefits as described in White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23.   To reduce delays and evidence problems, Forseti Legal Services helps you define the report scope with the requesting paralegal or lawyer, confirms the expert reviewed the right underlying documents (images, testing, and appendices) with clear cross-references, and helps structure the report with plain, readable language, a CV, a cover page, headings, page references, and an upfront conclusions summary while keeping the expert’s opinions impartial and evidence-grounded.   If you need a report prepared for court in Ontario, contact (705) 806-7577 for a consultation.

Understanding the Requirements When Preparing an Expert Witness Report Document for Court Litigation Purposes

Expert Witness Report: A Well Documented and Supported Opinion from a Subject Matter Expert Quality expert reports can make or break a civil litigation case; and accordingly, errors or omissions within an expert report, or in the manner of selecting an expert or in the manner of introducing an expert may preclude the expert report from evidence and preclude the opinion of the expert from testimony, thus placing the legal case in jeopardy.

The Law
Admissibility

For a court to admit an expert report as evidence the expert report must meet the criteria of admissibility.  The criteria was summarized within the case of 2599475 Ontario Inc. v 2549445 Ontario Inc., 2023 ONSC 3508, where it was said:


[35]  The test for the admissibility of expert evidence is based on the criteria set out in R. v. Mohan, 1994 CanLII 80 (SCC), 1994 SCC 80, as follows:

a)  Relevance;

b)  Necessity in assisting the trier of fact;

c)  The absence of any exclusionary rule, apart from the opinion rule itself; and

d)  A properly qualified expert.

[36]  In White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, [2015] 2 S.C.R. 182, the Supreme Court divided the admissibility requirement into two distinct steps.  First, a trial judge considers the four Mohan criteria.  Then the judge balances the potential risks and benefits of admitting the expert evidence.

Quality Expert Reports
Communicate Clearly and Effectively

Before the work of preparing a report begins, the expert should obtain a clear and concise understanding of the scope of detail required within the report by communicating directly with the lawyer or paralegal who is seeking the report from the expert; whereas, depending on the nature of the litigation, the required statements within the report may vary between just a general summary expert viewpoint or a highly detailed expert opinion. Failing to conduct this review may result in the expert wasting the effort of preparing an excessively detailed report or useless preparing an insufficient report; and whereas both possibilities may result in a waste of time, such is also a waste of money.

It is also necessary that the supporting evidence documents reviewed by the expert are adequately included and properly referenced.  The expert opinion contained within a report should, and perhaps must, refer to supporting evidence documents such as pictures or testing results, among other things, attached as appendices or schedules.  Additionally, a bibliography to summarize any authoritative documents used for research should be included.

The report should read clearly with ease and appear professional and proofed for proper spelling, grammar, and punctuation.  The expert should write in a style directed towards the intended audience, balancing need that the report be understood by an average layperson without belittling highly intelligent judges and lawyers or other experts.  Reports should omit or limit industry specific jargon and abbreviations; but, if such is necessary, include definitions within the report.

More Hints

  • Use professional letterhead;
  • Use a cover page as well as an index or table of contents;
  • Use a curriculum vitae or resume to summarize the qualifications and credentials that confirm that the expert is genuinely an expert;
  • Use an introduction page to outline when, and from whom, the report was requested;
  • Use 12-point font and double spacing;
  • Use headings;
  • Use short, concise paragraphs;
  • Use a unique reference number for each page, table, chart, and appendix;
  • Use a definitions page or section to define technical language and industry specific jargon or abbreviations; and
  • Use an upfront summary page to outline final conclusions or opinions.

Things to Avoid

An expert report must be impartial and objective.  The role of an expert is to provide an unbiased opinion to the court for the purpose of aiding in the truth-seeking mission of the court.  The expert must therefore ensure that the expressed opinion is grounded in facts and evidence rather than prepared with a favouring of a litigant.

  • Avoid absolute wording and phrasing;
  • Avoid words that appear as hedging or guessing;
  • Avoid critical commentary regarding credibility of other experts;
  • Avoid a scientific and clinical tone by keeping the tone friendly and personable;
  • Avoid going into details beyond the purpose of the report;
  • Avoid unnecessary adjectives or superlatives.

Summary Comment

The expert preparing an opinion report must remain attentive to the balance required when obtaining input from a legal representative whereas the lawyer or paralegal seeking the report will best understand the factual concerns and legal issues that relate to why the report is needed and can explain the desired scope; however, the findings and opinions as stated within the report must always remain the genuine unslanted view of the expert as author of the report.

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