Byrom's capital murder conviction was reversed, and the case has been remanded to the circuit court for a new trial, the opinion said.
"We are very grateful that the Mississippi Supreme Court has granted Michelle Byrom's request for relief from her death sentence," said Byrom's attorney, David Calder. "This was a team effort on the part of the attorneys currently representing Michelle, and we believe that the court reached a just and fair result under the facts presented in this case."
Byrom has been on death row since her 2000 conviction for capital murder. The 57-year-old woman was convicted of being the mastermind of a murder-for-hire plot to kill her allegedly abusive husband, a killing her son had admitted to committing in several jailhouse letters and, according to court documents, in an interview with a court-appointed psychologist.
He recanted when he was put on the stand, according to court records.
Attorney General Jim Hood, who had requested Byrom's execution, said Monday his office would seek the court's reasoning for the reversal.
"While we respect the Mississippi Supreme Court's decision, it is important that the trial court know and understand the specific errors that were found by the justices so that the lower court knows the best way to proceed," he said. "Our citizens can once again take comfort in the fact that we have a legal system that works for all parties involved."
The Supreme Court opinion noted that the decision "is extraordinary and extremely rare in the context of a petition for leave to pursue post-conviction relief."
Oliver Diaz, the former presiding justice of the Supreme Court, called the opinion "actually kinda amazing," from the order for a new trial to the ruling's release on a Monday instead of a Thursday, as usual.
"The lawyers filed a last ditch motion for additional post conviction relief. These are almost never granted. Defendants are limited to a single post conviction motion," he wrote in an e-mail to CNN. "It is extremely rare to grant and send back for a new trial."
The court further instructed that a different judge should be assigned to Byrom's new trial.
Circuit Judge Thomas J. Gardner, who imposed the death sentence on Byrom after her conviction, declined to comment to CNN, saying, "The matter is ongoing."
Diaz also said the order for a new judge was extraordinary.
"Also, taking the step of removing the original trial judge is very unusual as well," he wrote.
Tara Booth, spokeswoman for the Mississippi Department of Corrections, said the department expects an order Tuesday to transfer Byrom from the Central Mississippi Correctional Facility to Tishomingo County, where the killing occurred.
Hood, the attorney general, had requested that Byrom be executed "on or before (the date of) March 27," but the Mississippi Supreme Court, which has the final say on execution dates, denied Hood's request.
During Michelle Byrom's original trial, prosecutors said she plotted to kill her husband, who was fatally shot in his home in Iuka, Mississippi, in 1999 while Michelle was in the hospital receiving treatment for double pneumonia. A jury convicted her based on evidence and testimony alleging that she was the mastermind of the plot.
Byrom Jr. admitted in jailhouse letters that he had committed the crime on his own after growing tired of his father's physical and verbal abuse, and a court-appointed psychologist has said that Byrom Jr. told him a similar story.
On the stand, Byrom Jr. pinned the slaying on one of his friends, whom he said his mother had hired for $15,000.
Following her attorney's advice, Michelle Byrom waived her right to a jury sentencing, allowing the judge to decide her fate. He sentenced her to death.
Prior to Monday's ruling, Michelle Byrom's defense attorneys had filed a motion asking the court for additional discovery so the alleged confession to the court-appointed psychologist could be fully explored.
The defense attorneys also want to depose the prosecutor from her trial, Arch Bullard, regarding his knowledge of Byrom Jr.'s alleged confession to the psychologist.
Bullard has told CNN that he firmly believes Michelle Byrom was the mastermind of the murder-for-hire plot.