What is the Role of an Expert Witness in a Trial?

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In a trial, an expert witness plays a critical role in helping to clarify complex technical or scientific information for the court and jury. The information provided by expert witnesses can have a major impact on a trial’s outcome, as their knowledge and experience can be used to support or challenge arguments presented by either side.

Expert witnesses are an important part of the legal process – they bring specialized expertise in a specific area, like medicine, engineering, law, forensics, and more. They can be called upon by either the plaintiff or the defendant’s team to offer their professional opinion and insights related to the case. They often provide evidence or testimony in the courtroom.

The Role of an Expert Witness

Expert witnesses provide objective and impartial testimony based on their knowledge and experience. Their testimony must be based on scientific or technical principles that are accepted by the relevant professional community, and their opinions must be supported by data or other evidence.

One of the key responsibilities of an expert witness is explaining complex technical, legal, medical, or scientific concepts in a way that the jury can easily understand. This could include breaking down complex terminology or theories into more concise language or using visual aids (diagrams or charts) to demonstrate their points.

As part of the trial process, expert witnesses also often face cross-examination by opposing counsel. Experienced expert witnesses are prepared for this challenging part of the process, which could involve opposing counsel attempting to downplay the expert’s experience, credibility, or opinions. The expert witness must be able to defend their opinions and clearly explain the reasoning behind them, even during a high-stakes, intense trial situation.

What is an Expert Witness’s Duty?

One crucial distinction is that expert witnesses are not supposed to be advocates for either side in the case, no matter who is paying their fee, though in reality they often are.

While they may be called upon to provide testimony that supports one side or the other, their primary responsibility is to provide objective and impartial testimony based on their knowledge. Expert witnesses may also provide written reports or other documentation related to their opinions.

How to Select an Expert Witness

Attorneys must carefully consider the qualifications and experience of potential expert witnesses, and choose individuals who have a proven track record of providing reliable and objective testimony. Not just anyone can be an expert witness – it requires years in their field, along with substantial courtroom experience.

Before being hired, the expert witness will likely have to provide:

  • Their career history, CV, and/or resume
  • An account of their experience as an expert witness
  • Details about their participation in past trials, mediations, arbitrations, or other legal experience
  • Examples of previous written reports, documentation, etc. that supports their position as an expert in their field

Legal Expert Witness Services in California

If you are interested in hiring a legal expert witness, Tim McGonigle has extensive experience in the area. With over 35 years of experience as a trial attorney in California, he has served as an expert witness on numerous legal matters.

Feel free to reach out to The McGonigle Law team with any questions.


The information contained herein is for general purposes only and does not constitute legal advice.


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