What Is An Expert Witness?

Posted in Forensics and Investigations on January 23, 2024
What Is An Expert Witness?

What is an expert witness? An expert witness is a person with knowledge and experience of a particular field or discipline that a layman cannot expect. The responsibility of an expert witness is to give an impartial opinion on particular aspects of matters which are in dispute to the court.

An expert witness is a person whose opinion is accepted as an expert by the judge due to education, training, certification, skills, or experience, particularly in common law countries such as the United Kingdom, Australia, and the United States.

What Is An Expert Witness?

What Is An Expert Witness?

An expert witness is not an expert adviser who is normally appointed by a party to assist in the formulation and preparation of a party’s claim or defense because an expert adviser does not have an overriding duty to the court but to the party instructing him.

The primary function of an expert witness is to express his independent opinion based on the provided information. An expert can be employed in different capacities, for example, at arbitrations, tribunals, and litigation.

A witness is a person giving sworn evidence to a court of law. There are two types of witnesses; witnesses of fact who may give evidence of fact but may not normally give opinions, and expert witnesses who may give opinion evidence within their expertise in addition to evidence of facts.

A qualified expert witness is someone who has knowledge, skill, education, experience, or training in a specialized field, according to the Federal Rules of Evidence. These qualifications are usually required of expert witnesses in state courts as well.


An expert witness must meet the following requirements in order to be admissible:

  • Work in a profession related to the case’s issue
  • be knowledgeable about their field
  • Have specialized knowledge gained through education, training, or practical experience

The expert is qualified to give an opinion on the case if and only if his or her professional knowledge and skill set will help the jury understand the evidence better. The expert’s knowledge must be superior to that of the jury. He or she does not have to be the best in the field or know every detail about the case, as long as his or her expertise is relevant.


The expert’s testimony as an expert witness must be based on:

  • adequate data and factual information
  • accepted principles and methods widely used in the field
  • Appropriate use of the principles and methods

The expert’s testimony is admissible if he or she uses unambiguous data and adheres to the standard of practice in his or her field of expertise.


By assisting the fact finder, an expert must be able to add value to the case. As a result, the expert testimony must:

  • Provide a credible opinion to assist fact-finders in reaching a decision.
  • Include valid scientific connections to case evidence that were previously unknown.

If an expert’s assumptions do not apply to the facts of the case, he or she is not considered useful. The expert must provide new and unexpected information to the jury, while also ensuring that there are no analytical gaps in their reasoning.


The expert’s opinion must be founded on fundamental facts that have been agreed upon by other experts in the same field. The facts on which the expert bases their conclusion must be correct and relevant to the issue at hand.

Final Thoughts

Expert witness testimony can have a significant impact on the judge’s final decision. As a result, Federal Rule of Evidence (FRE) 702 strictly defines expert admissibility standards. Rule 702 defines (a) the qualifications of expert witnesses and (b) the level of admissible testimony in detail. Only when all four primary pillars defined in the FRE 702 does an expert meet the standards of a reliable expert witness.