McWilliams v. Dunn, 582 U.S. 183 (2017), is a United States Supreme Court case in which the court held that, when the conditions of Ake v. Oklahoma are met, the state must provide a defendant with access to a mental health expert who is sufficiently available to the defense and independent from the prosecution to effectively conduct an appropriate examination and assist in evaluation, preparation, and presentation of the defense.

James E. McWilliams was an incarcerated person on death row. He was convicted of various crimes including murder, rape, and robbery.

The Court ruled 5–4 in favor of Williams on the grounds of the defendant not having access to an independent mental health expert during his trial with the lower appellate court not considering this in the previous appeal, as written in the opinion authored by Justice Breyer.

This article incorporates written opinion of a United States federal court. As a work of the U.S. federal government, the text is in the public domain.