A prisoner in Georgia who has been diagnosed as intellectually disabled by all medical experts who have examined him will be put to death on Monday unless the US supreme court acts to enforce its own constitutional ban on executing "mentally retarded" individuals.

Only the supreme court now stands between Warren Hill and death, all other legal options having been exhausted in recent weeks. "The supreme court is probably the last stop, period," said the lawyer for the condemned man Brian Kammer, who is waiting to hear whether the court will consider his petition.

Hill, 52, is scheduled to be killed with a single injection of the sedative pentobarbital at 7pm on Monday in his second appointment with the death chamber in just five months. In February he came within 30 minutes of execution before the procedure was stayed.

Hill's execution would be a flagrant violation of the US supreme court's own ruling in 2002, Atkins v Virginia, that banned the death sentence for prisoners classified as "mentally retarded". The ruling left a tiny gap through which death penalty states could wriggle by leaving it up to them to define the legal standard under which "mental retardation" – known in modern medical parlance as intellectual disability – is defined.

Georgia is the only state that insists on the highest legal bar possible: "beyond a reasonable doubt". Yet even in that regard Warren Hill has been found to meet the definition – he has an undisputed IQ of 70 and all nine medical experts who have diagnosed him over the years have declared him to fall into the "mental retardation" category beyond a reasonable doubt.

In July 2012 a doctor who had examined the prisoner in 2000 and deemed him not to be intellectually disabled had voluntarily approached the defence team and reported that in the light of modern understanding of mental development he had changed his opinion. "Now there's absolutely no disagreement between any of the experts," Kammer told the Guardian.

Hill's execution would be a clear violation of the Eighth Amendment ban on cruel and unusual punishment, as ruled by the US supreme court itself in Atkins v Virginia. In that ruling the nation's highest judicial panel noted that intellectual disability placed prisoners at "special risk of wrongful execution".

But Hill has fallen into a form of legal limbo. All of Georgia's state courts have now refused to rehear his case, as has the body that is supposed to act as a fail-safe, the Georgia State Board of Pardons and Parole.

The federal 11th circuit court of appeals has also declined to hear the case because of a legal technicality that puts Hill in a Catch-22. The court ruled that it cannot stop the execution even if a glaring mistake was made in his death sentence unless the new evidence related to the prisoner's innocence; in this case it does not speak to innocence but to the state of his mental development.

A federal judge sitting on the appeals court, Rosemary Barkett, gave a dissenting ruling in which she said "the idea that courts are not permitted to acknowledge that a mistake has been made which would bar an execution is quite incredible for a country that not only prides itself on having the quintessential system of justice but attempts to export it to the world as a model of fairness."

Hill's guilt is not in question. In 1990 he was already serving a life sentence for murdering his girlfriend when he killed fellow inmate John Handspike in a Georgia prison, beating him to death with a nail-studded board.

The impending execution has led to an outpouring of protest from numerous individuals and organisation. Those calling for a stay include former US president Jimmy Carter, the Council of Europe, the president of the American Bar Association, a group of mental disability experts, a group of law professors and a raft of human rights groups.