Mississippi Attorney General Jim Hood had asked the court to void those pardons, among some 200 issued by the former Republican governor in January, on the grounds that technical procedures set out in the state constitution had not been met.
But the state Supreme Court ruled 6 to 3 that it could not set aside the contested pardons based solely on Hood's claim that the prisoners had failed to meet an obscure provision requiring felons seeking a pardon to publish the request in a newspaper 30 days in advance.
Hood, a Democrat, was not able to show that any of the pardons were invalid on their face, presiding Justice Jess H. Dickinson wrote in the majority opinion.
Like many states, Mississippi allows its governor to issue pardons with virtual impunity. Lawyers for the people pardoned had argued the court did not have the authority to overturn the pardons.
"At the outset, we wish to state that this case is not about whether the governor is above the law," Dickinson wrote. "He clearly is not..."
"We are compelled to hold that - in each of the cases before us - it fell to the governor alone to decide whether the Constitution's publication requirement was met," Dickinson said.
The 10 people who received the contested pardons were all prisoners at the time. Five had worked at the governor's mansion doing odd jobs, and four of those five inmates were serving life sentences for murder.
Half of the 10 remain behind bars due to a temporary restraining order that kept them imprisoned while Hood's challenge was under review.
The court vacated the restraining order on Thursday, but it was unclear when the prisoners would be released.
A spokeswoman for the state Department of Corrections said it must notify local law enforcement, prosecutors and any registered victims 48 hours before releasing the inmates.
The cases at issue in the legal challenge were not the only pardons by Barbour, a former Republican National Committee chairman, to spark controversy.
About two-thirds of the pardons were to whites and a third to blacks. Mississippi's prison population is roughly the reverse, two-thirds black and a third white.
One of the people pardoned was the brother of former National Football League quarterback Brett Favre. Earnest Scott Favre was convicted in 1996 of driving while intoxicated after a vehicle he was driving crashed and killed his best friend.
Favre was not in prison at the time of his pardon.
In a statement on Thursday, Barbour applauded the court's decision to uphold the governor's right to exercise not only clemency but also mercy.
"As I've stated from the beginning, I recognize and respect the natural feelings of victims and their families and I know this has been difficult for many of them," Barbour said.
"Nevertheless, these were decisions based on repentance, rehabilitation, and redemption, leading to forgiveness and the right defined and given by the state constitution to the governor to offer such people a second chance."
Hood said he would seek to change the constitution to require courts to enforce the 30-day notification policy in the future. He did not say whether he would challenge more of Barbour's pardons as he previously had indicated he would do.
"We do respect the decision of the Court, but feel deeply for how it must weigh on the victims and their families," Hood said in a statement on Thursday. "It is these victims and family members who have lost today and the criminals who have won."
The ruling shows the state's high court will not "police" other branches of government on procedural requirements, said Matthew Steffey, a constitutional law professor at Mississippi College who has followed the case.
"I believe the majority opinion is more faithful to constitutional history, precedent and theory," he said. "It's a principle of separation of powers."
(Writing by Colleen Jenkins; Editing by Greg McCune; Desking by Eric Walsh)
