No expert testimony about the law

The Texas Supreme Court addressed the important topic of expert testimony about legal issues in In re Lopez. It held that the trial court improperly admitted a former judge’s expert testimony on whether an informal marriage existed because (1) the issue was within the common knowledge of jurors and (2) the witness offered legal opinions and judicial imprimatur (she was a former judge) rather than helpful expertise.

The Court emphasized that the expert repeatedly told the jury how she would rule “wearing [her] judge’s hat,” opined on a legal presumption, and thereby provided “an official endorsement” of one side’s position—testimony Rule 702 does not permit. The Court concluded the error was harmful and ordered a new trial. No. 24-0315 (Tex. Nov. 7, 2025).