A lawyer serving as an expert witness to testify on behalf of a party who is another law firm’s client, as distinct from an expert consultant, does not thereby establish a client-lawyer relationship with the party or provide a “law-related service” to the party within the purview of Model Rule 5.7 such as would render his services as a testifying expert subject to the Model Rules of Professional Conduct. However, to avoid any misunderstanding, the testifying expert should make his limited role clear at the outset. Moreover, if the lawyer has gained confidential information of the party in the course of service as a testifying expert, the lawyer may as a matter of other law have a duty to protect the party’s confidential information from use or disclosure adverse to the party.

Model Rules 1.7(b) and 1.10(a) apply to the lawyer’s representation of a client adverse to a party for whom he is serving as a testifying expert. If the duty of confidentiality to the party on whose behalf the lawyer serves as a testifying expert would “materially limit” the responsibilities of the lawyer to one of his clients, the lawyer and any firm with which the lawyer is associated may be prohibited from concurrently representing that client. Ordinarily it would not be reasonable for the lawyer to believe in those circumstances that the representation of the client will not be adversely affected, and if so, client consent does not permit the representation. Moreover, even though these requirements of the Model Rules are satisfied, other law, including the law of client-lawyer privilege and the law of agency, may prohibit the lawyer and his law firm from representing the client, unless the party on whose behalf the lawyer serves as a testifying expert waives its right to object.

After the testifying expert relationship has concluded, the testifying expert and his law firm may be precluded from representing a client in a matter in which use of the party’s confidential information would be necessary. Model Rules 1.9(a) and 1.9(c) do not apply because the party for whom the lawyer was asked to testify is not a former client. Nevertheless, the responsibilities of the lawyer under other law to maintain the confidentiality of the party’s information may materially limit the representation in the subsequent matter, and it may not be reasonable for the lawyer to believe that the representation would not be adversely affected; if so, Model Rules 1.7(b) and 1.10(a) would bar the subsequent representation.