U.S. — The Supreme Court ruled in Hunter v. United States that a federal defendant's waiver of appellate review is unenforceable if enforcing it would result in a miscarriage of justice. The Court did not determine if such a miscarriage of justice would occur in the specific case.

Justice Elena Kagan's opinion, joined by six other justices, stated that an agreement not to appeal a sentence is unenforceable when it would result in a miscarriage of justice—meaning, when it would leave in place the kind of egregious error that would bring the judicial system into disrepute. Kagan wrote that standard-fare errors in misapplying sentencing law cannot cancel an appeal waiver.

The majority described the circumstances where the miscarriage of justice standard would be met as rare and involving extreme cases. Kagan stated that an appellate waiver would not prevent a defendant from appealing a sentence exceeding what the relevant statute allows. She noted appeals are permitted for a blatant constitutional error, such as when a judge takes account of a constitutionally impermissible factor like race. Appellate waivers could also not be enforced when a sentence was imposed without some minimum of civilized procedure.

Kagan's opinion did not rely on principles of contract law. She pointed to a district court's role under Federal Rule of Criminal Procedure 11(c)(3)(A) in accepting a plea agreement and federal courts' institutional interest in ensuring that legal proceedings appear fair. She wrote, "Sentencing is a complex affair in our criminal justice system, involving for example the detailed calculation of a Sentencing Guidelines range and the mandatory consideration of multiple sentencing factors."

Munson Hunter pleaded guilty to one fraud count stemming from a decade-long financial scheme which caused losses of nearly a half million dollars. In exchange for his plea, the government dismissed nine fraud counts, and Hunter agreed to waive his right to direct appeal and collateral review, except for claims of ineffective assistance of counsel. He was sentenced to 51 months of imprisonment. Hunter filed a direct appeal challenging a special condition of his supervised release requiring him to take medication prescribed for his depression and anxiety but did not contest his term of imprisonment.

The U.S. Court of Appeals for the 5th Circuit previously dismissed Hunter's appeal, relying on his appellate waiver. The Supreme Court rejected Hunter's contention that the prosecutor's failure to object to a statement made at the sentencing hearing constituted a waiver by the government. The plea agreement stated it could only be modified in writing, which did not occur, and the government's silence did not constitute an affirmative signal of abandonment, Kagan said.

Justice Amy Coney Barrett concurred in an opinion addressing the scope of supervisory powers. Justice Clarence Thomas dissented, highlighting that Kagan's opinion never explicitly stated reliance on supervisory powers.