"We are greatly relieved that the Eleventh Circuit Court of Appeals has stayed the execution of Warren Hill, a person with mental retardation. All the doctors who have examined Mr. Hill are unanimous in their diagnosis of mental retardation," defense attorney Brian Kammer said in an email.
A spokeswoman for the state attorney general declined comment.
Hill was sentenced to die for the 1990 beating death of fellow inmate Joseph Handspike. Authorities say he used a board studded with nails to bludgeon Handspike while he slept and other prisoners pleaded with Hill to stop. At the time Hill was already serving a life sentence for murder in the 1986 slaying of his girlfriend, Myra Wright, who had been shot 11 times.
Hill has received support from various activists and from former President Jimmy Carter and his wife Rosalynn.
"Georgia should not violate its own prohibition against executing individuals with serious diminished capacity," President Carter said in a statement.
Hill was originally set to be executed in July, but the state delayed his execution when it changed its execution procedure from a three-drug combination to a one-drug method. The state Supreme Court then further delayed the execution after Hill's lawyers filed a challenge saying corrections officials violated administrative procedure when they made the change. The state's high court earlier this month denied that challenge, and Hill's execution was reset for Tuesday.