Given Brady v. Maryland and the rules of professional conduct related to the special responsibilities of prosecutors you would think this is self evident. But it isnt. Some courts have held that a defendant can't challenge the validity of a guilty plea by arguing a Brady violation. In Huebler, the court explains that "[t]his issue arises because Brady evolved from the due-process guarantee of a fair trial, . . . and therefore has been described as a trial right, . . . but when a defendant pleads guilty, he waives several constitutional guarantees, including the due-process right to a fair trial, and any errors that occurred before entry of the plea."
After discussing the conflicting case law, the court agreed with other courts that have held that not requiring prosecutors to disclose exculpatory evidence before negotiating plea agreements could tempt prosecutors to deliberately withhold exculpatory information as part of an attempt to elicit guilty pleas. In the end, the court concluded that
"[w]hile the value of impeachment information may depend on innumerable variables that primarily come into play at trial and therefore arguably make it less than critical information in entering a guilty plea, the same cannot be said of exculpatory information, which is special not just in relation to the fairness of a trial but also in relation to whether a guilty plea is valid and accurate. For this reason, the due-process calculus also weighs in favor of the added safeguard of requiring the State to disclose material exculpatory information before the defendant enters a guilty plea.
It is not every day that an innocent person accused of a crime pleads guilty, but a right to exculpatory information before entering a guilty plea diminishes the possibility that innocent persons accused of crimes will plead guilty."