Who can be an expert witness & different types of expert witness.


The question of who can be an expert witness will best be answered by first knowing what an expert witness means. An expert witness can be anyone with advanced knowledge and experience of a particular discipline beyond that expected of a novice.

The duty of an expert witness is to give the court a disinterested, unbiased and impartial opinion on a particular matter within his field of knowledge and expertise.

The primary function of an independent witness is to express his independent opinion based on the information made available to him. There are basically two types of witnesses, namely;

The witness of fact; this is the witness who testifies on fact known to him or her an expert witness who gives the court an independent opinion on his area of expertise based on the information made available to him.

An expert witness is expected to provide an expert opinion in his area of expertise based on the information provided to him.

An expert witness must provide his opinion in the form of an expert opinion report. Where he failed to prepare it as a report, he may not be allowed to give his opinion.

The expert witness owes a serious duty to the court to provide a disinterested opinion to the court more than he owes the person who called him and who pays his expert witness fees.

An expert witness must never argue in a case. It is not his duty to argue in court as an advocate. He must never provide advice to any party. He must not provide any opinion beyond his field of expertise. He must not act as a negotiator.

An expert witness can either be a party-appointed expert witness or a single joint expert. An expert witness is a party-appointed expert where he is appointed and instructed by one of the parties to the case while he is a single joint expert where he is appointed by both parties to the case. There is also an expert adviser otherwise called shadow expert. This one is appointed by one of the parties to advise them in the dispute.

Note, as an expert witness, if u are deposed as an expert in a case, you can rightly charge a fee as an expert witness fee.

As an expert witness, u are expected to give the court your expert opinion only on your field of expertise and you must be sure that you are so qualified as you have represented to the court.



To appreciate the different types of expert witnesses, we need first of all to know who an expert witness is. An expert witness is a person qualified, specialized, experienced, advanced or knowledgeable in a particular field, either medical field, accounting field, etc being invited to court to give an expert unbiased and disinterested opinion on his area of expertise based on the information made available to him.

An expert witness coming to court to testify can either be a party-appointed expert witness or a single joint expert witness.

There are generally different types of an expert witness;
  1. MEDICAL EXPERT WITNESS-: Medical expert witness seem to be the most common type of expert witness. These are experts from different medical fields. They are invited to provide a professional medical expert opinion in cases of medical malpractice, medical violent crime trial or in any other trial where medical expert opinion is needed like rape cases etc depending on the witness’ area of specialization. Often times medical doctors do this work of medical expert witness, however, sometimes nurses, physician’s assistants, laboratory assistants and other medical experts also do same.
  2. ACCOUNTING AND SECURITIES EXPERT WITNESSES-: These expert witnesses provide expert opinion on more complex matters dealing on white collar crime and fraud. Aside crimes, they also advise courts on when a particular company falls short of their duties and obligations to their customers. They also come in when banks engage in crimes, frauds and misappropriation and mismanagement of customers’ money and when they fail in their banker/customer relationships.
  3. FORENSIC EXPERT WITNESS:- Forensic science is the application of science to criminal and civil laws, especially on criminal aspects during investigations as governed by legal standards of admissible evidence and criminal procedure.  In as much as there seems to be an overlap in the functions of medical and forensic experts, forensic experts range from biologists, chemists, psychologists etc. Forensic experts are usually employed by most law enforcement agencies to provide expert opinions and also testify in court when the need arises.
  4. VOCATIONAL EXPERT WITNESS:- These experts are called by the social security administration when someone petition a denial of social security disability benefits.  On normal circumstance, the social securities administration always deny benefits to the disabled individuals on the ground that they cannot work. If the disabled individual then petitions that he can work despite his or her disability, the vocational experts are invited to give an expert opinion as to whether such a disabled individual can work.  It should be noted that unlike other experts that need to have special knowledge and training, vocational expert witnesses do not need to have any special qualification or training to hold the job. This always makes lawyers to treat them with suspicion.
  5. MENTAL HEALTH EXPERT WITNESS:- These are very similar to medical experts. However mental health experts are invited to give an expert opinion as to the mental fitness or otherwise of a suspect in a trial.

Knowledge of the different types of an expert witness, scope and function is useful in knowing which particular expert to invite in cases where expert opinion is needed.

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Author: Chibuzor Onuorah

Nigerian Law School, Bwari, Abuja.