The execution of Walter Moody is planned for 6 pm CDT (2300 GMT) at the William C. Holman Correctional Facility in Atmore. He would be the eighth inmate put to death this year in the United States.
If the execution is carried out, Moody would replace John Nixon, who was 77 when put to death in December 2005 in Mississippi, as the oldest person executed since the US Supreme Court reinstated the death penalty in 1976, according to the Death Penalty Information Center, which monitors US capital punishment.
Moody was convicted of mailing a bomb in 1989 that killed US Circuit Court Judge Robert Vance, 58, and another explosive that killed Georgia civil rights attorney Robert Robinson.
Prosecutors have said Moody sent the bomb to the judge in anger over a 1972 bomb conviction that Moody felt derailed his career, and sent the other to the civil rights lawyer to confuse investigators.
Moody, who has spent more than 20 years on death row, has maintained his innocence and his lawyers have not yet used his age in appeals seeking to halt the execution. He has applied for clemency at the state level.
Lawyers for Moody filed last-minute appeals with the US Supreme Court to spare Moody's life based on his transfer from the federal court system to Alabama's.
Moody's lawyer argued the transfer to an Alabama prison was illegal and he should first serve his federal sentence, asking the Supreme Court to halt the execution.
Lawyers for Alabama responded that the federal government consented to the transfer and the state had the right to implement the death penalty handed out by an Alabama court.
Age and poor health were major factors in a botched execution in Alabama earlier this year when the state tried to put to death Doyle Hamm, 61, who had terminal cancer and severely compromised veins.
The execution was called off while Hamm, who survived the ordeal, was on a death chamber gurney and medical staff could not place a line for the lethal injection.