Calling your Former Lawyer as an Expert Witness Waives the Attorney-Client Privilege

If you choose to call your former lawyer as an expert witness, you should not be surprised if the court holds you have waived the attorney-client privilege, at least with regard to any prior communications about the topics on which they will testify. In Cummings v. Deloitte Tax LLP, Mass. Super. Court Docket No. 23-103-BLS1, Jan. 16, 2026, Business Litigation Session Judge Peter Krupp granted a motion to compel production of documents and to require the attorney to answer questions at a deposition about topics that might otherwise have been privileged.

The case is an accounting malpractice action against Deloitte, alleging mistakes in connection with the plaintiff’s tax returns. The plaintiff’s attorney defended the plaintiff (apparently unsuccessfully) in connection with an IRS audit. The plaintiff then designated that same attorney as its expert witness in the malpractice action against Deloitte. The proffered expert opinion was at least arguably inconsistent with the contentions the expert advocated to the IRS. Because the plaintiff chose to have its former attorney also act as its expert witness, the court held that it had waived the attorney-client privilege and work product doctrine with regard to prior communications and documents relating to those same opinions.

The obvious take-away here is to think carefully about whether calling your attorney as an expert witness may have unintended consequences – a waiver of the attorney-client privilege.