Using expert opinion as evidence in Supreme Court

Supreme Court

Evidence is the information you use in court to convince the judge to make the order you've asked for. The judge decides what evidence can or can't be presented in (shown to) court.

One way to present your evidence is by getting an expert opinion.

Regular witnesses can't usually give their opinions in court. But a qualified expert can give an opinion based on:

  • what they've seen or learned directly, or
  • information other people gave them.

Their opinion has to give the court information that the judge wouldn't normally know (for example, about certain health conditions).

An expert witness has special knowledge of a certain area because of their:

  • training,
  • education, and
  • work experience.

For example, a psychologist who has training and experience in dealing with children going through separation and divorce could be an expert witness when it comes to deciding where the children should live.

An expert's duty is to help the court. It's not to be on one person's side. In fact, in family law, experts who give evidence on financial issues have to be chosen by both people involved in the case. See Supreme Court Family Rule 13-3 for more about this.

The rules about using an expert witness at a trial are complicated. It's a good idea to speak to a lawyer if you plan to do this. Some lawyers now offer unbundled legal services, which means you can pay them to help you with part of your family law problem, and you handle the rest of your case yourself.

But here are some basic rules to get you started:

  • If you want to call an expert as a witness at your trial, they have to write a report about the issue they're going to talk about.
  • You need to give the report to the other person in your case at least 84 days before the trial date.
  • Either you or the other person can have the expert come to the trial to give evidence. If no one wants the expert to give evidence at the trial, you can still ask the judge to let you use their report. See Supreme Court Family Rule 13-7 to find out more about this.
  • If you or the other person wants to call a person who prepared a report under section 211 of the Family Law Act about the needs and views of the children, they have to serve that person and all the other people involved with a Notice to cross-examine (Form F43) at least 28 days before trial.


How do you cross-examine an expert witness?

If you call the expert to trial to be cross-examined (that is, they'll be asked questions), you can ask them questions to challenge their report. For example, you might want to ask the expert questions about:

  • their qualifications (why they're an appropriate person to give an opinion on a certain issue),
  • their opinion,
  • what facts they looked at when they were forming their opinion, or
  • what tests or experiments they used to help them form their opinion.

See Sample questions to ask when cross-examining witnesses at a Supreme Court trial for more detail about this.


A 5½-minute video describing how to prepare your spoken testimony, present it in Supreme Court, and respond to questions from the judge and the other party.
Updated on 21 October 2020