Attorney General Steve Marshall's office says the ruling doesn't matter and Arthur's execution will go forward. Arthur's lawyers argued that Smith was awake during his execution.
Arthur was found guilty of conspiring with his then-lover Judy Wicker to murder her husband Troy so that she could cash in on his life insurance.
Tommy Arthur's lethal injection is scheduled for 6 p.m. CDT (7 p.m. ET) in Atmore, Alabama.
The sprawling case began February 1, 1982, when police responded to a call about a break-in and found riverboat engineer Troy Wicker slain in his bed in the north Alabama city of Muscle Shoals.
Wicker's two sons witnessed the execution but did not make a statement to the media.
After going through three separate trials for Wicker's murder, Arthur has pursued dozens of appeals in state and federal courts. She said she paid him 10,000 United States dollars. Ultimately, the sentenced to the death penalty, Tommy Arthur, was executed in the prison held in Alabama, USA.
An officer performed a test to determine whether intravenous drugs had rendered Arthur unconscious about 3 minutes before his death warrant expired, saying the inmate's name repeatedly and pinching his arm without a visible response.
No physical evidence links Arthur to the murder, and Alabama has refused to allow DNA testing of a wig worn by the killer, his lawyers have noted. A second conviction followed and also was overturned, but he was convicted a third time and sentenced to death.
Arthur was a work release prisoner at that time.
The state responded in a court filing that there was no evidence that Smith, or other inmates, experienced pain.
In new appeals, Arthur said Alabama in December injected inmate Ronald Smith with painful execution drugs while Smith was still conscious.
In his last 24 hours, Arthur had no visitors, according to Department of Corrections public information officer Bob Horton.
Wicker's wife, Judy, initially told police she came home and was raped by a black man who shot and killed her husband.
The 11th U.S. Circuit Court of Appeals rejected a stay requested by Arthur.
The state attorney general said Arthur used perpetual litigation to avoid his sentence for years.
"As you know, the fact that the hair samples in question did not come from Mr. Arthur has never been in dispute".
Alabama death row inmate Tommy Arthur is asking the U.S. Supreme Court to block his execution set for Thursday night.
Throughout the evening Thursday, there was a possibility that Arthur would escape yet another execution date. She later changed her story, testifying that she paid Arthur $10,000 to kill her husband and that he painted his face black and wore a wig when he committed the crime. They also said advanced DNA testing, if conducted, could point to another suspect.