This question has been addressed in 1 Texas court opinion:
COA02 — February 19, 2026
In Ex Parte Robert Brimmer, a medical doctor sought to vacate his negotiated guilty plea through a writ of habeas corpus, arguing he was mentally incompetent at the time of the plea due to "distorted thinking" and paranoid delusions. The Second Court of Appeals analyzed the claim using the criminal competency standard, which requires a defendant to have a rational and factual understanding of the legal proceedings. The court affirmed the trial court's denial of relief, holding that the applicant failed to prove incompetence by a preponderance of the evidence. The court emphasized that contemporaneous forensic evaluations and affirmations of competence by trial counsel carry significant weight, and that the presence of mental illness or "unreasonable" legal beliefs does not automatically render a party legally incompetent if they understand the terms of the agreement.
Litigation Takeaway
“A party seeking to set aside a settlement based on a lack of capacity face a high hurdle; legal incompetence requires a functional inability to understand the proceedings rather than just a mental health diagnosis or 'distorted thinking.' Practitioners can 'competency-proof' agreements by securing contemporaneous affirmations of understanding from all parties and counsel at the time of execution.”