VARNER, Ark. — Hours before the state hoped to carry out its first execution in more than a decade, the Arkansas Supreme Court on Monday moved to block the inmate from being put to death.

The decision was a significant setback for the State of Arkansas, which had sought to execute eight men this month, before its stock of a lethal injection drug expires.

The Supreme Court announced its 4-to-3 decision as state officials and reporters gathered at the Cummins Unit for the execution of Don W. Davis, who was convicted more than a quarter-century ago of a murder in northwestern Arkansas.

The executions of Mr. Davis and the other prisoners had already been stayed by a federal judge who was concerned about Arkansas’s use of a particular injection drug. Not long after the State Supreme Court’s decision, however, the United States Court of Appeals for the Eighth Circuit, in St. Louis, reversed the federal judge’s order, removing that obstacle to the executions.

The reprieve from the justices in Little Rock was appealed, but defense lawyers said it lowered the odds that anyone would be put to death on Monday night. The state court ruling did not immediately affect the five other executions the Arkansas authorities hope to carry out by April 27. (Other litigation had resulted in stays of execution for some prisoners.)

A spokesman for the Arkansas Department of Correction said state officials were proceeding as if the execution would take place sometime Monday.

Gov. Asa Hutchinson said the state had “asked the U.S. Supreme Court to overrule the Arkansas Supreme Court” and hoped to get a decision within hours.

The argument that prompted Monday’s stay focused on a matter entirely different from the constitutional questions that have swirled around the state’s execution procedures and an injection drug, midazolam. Critics of the drug have argued that midazolam, a sedative, fails to render a prisoner sufficiently insensate to the pain of other medicines in lethal injections.

Instead, the Arkansas justices considered whether Mr. Davis should be put to death while the United States Supreme Court hears a case about whether poor defendants with mental health problems are entitled to expert witnesses to assist them in preparing and presenting their cases.

Although the Supreme Court has never directly addressed whether such experts must be independent of prosecutors, the justices had long planned to hear arguments on that question next week in a case involving a prisoner from Alabama, James E. McWilliams. The possibility of a ruling that would affect Mr. Davis’s case, the Arkansas justices concluded, was enough to warrant stopping his execution.

The ruling also applies to Bruce Ward, an Arkansas prisoner whose execution, originally scheduled for Monday, was already the subject of a stay.

“Both Mr. Ward and Mr. Davis were denied independent mental health experts to help their defense attorneys investigate, understand and present these critical mental health issues to the jury,” Scott Braden, an assistant federal defender who represents both men, said in a statement. “The Arkansas Supreme Court recognized that executing either man, before the court answers this question for Mr. McWilliams, would be profoundly arbitrary and unjust.”

The Alabama case that will go before the Supreme Court next week involves claims by Mr. McWilliams’s lawyers that his rights were violated when a court-appointed psychologist prepared a report that was distributed to both sides. Lawyers for the state responded that there is no right to a “partisan psychiatrist” and that “a neutral court-appointed psychiatrist who is equally available to both parties” is sufficient.

A decision in that case is expected by June. But the Arkansas court’s choice to stop Mr. Davis’s execution could extend his case for much longer, especially because the state is on the verge of having part of its drug supply lapse.

Mr. Davis did not seek executive clemency for his conviction for the death of Jane Daniel, whose husband found her in a pool of blood at home in Benton County.

“Somebody got hurt,” Mr. Davis told his roommates after the October 1990 murder, according to a court ruling. He fled west and was arrested in New Mexico.

“What I did was an act of cowardice,” Mr. Davis said in an interview with an Arkansas television station in 2015. “It was coldblooded. It was evil. The day I was found guilty in Bentonville, if they would have took me out that next day and executed me, I feel as though it would have been a just execution.”

Recalling Ms. Daniel’s murder, Mr. Davis also said in that interview, “There is nothing in this world that I wouldn’t give to change that moment.”

Mr. Davis has repeatedly faced the threat of lethal injection — he came within hours of being put to death in 2010 — and Ms. Daniel’s daughter noted last month that she had traveled to Pine Bluff, near the prison, four times for executions that were eventually called off.

Even on a day when he won some relief, Mr. Davis had his last meal, the prison spokesman, Solomon Graves, said. Mr. Davis ordered a meal that included fried chicken, mashed potatoes and strawberry cake.

In a sharply worded dissent, Associate Justice Shawn A. Womack complained about the delay that would allow Mr. Davis and Mr. Ward, who was also convicted of capital murder, to live.

“The petitioners had their day in court, the jury spoke, and decades of appeals have occurred,” Justice Womack wrote. “The families are entitled to closure and finality of the law.”

In a separate order on Monday, the Arkansas justices forbade a circuit court judge in Pulaski County, Wendell Griffen, from hearing cases related to capital punishment after he participated in a protest against the death penalty last week. The State Supreme Court also referred Judge Griffen to the Arkansas Judicial Discipline and Disability Commission.

The episode involving Judge Griffen, who on Friday ruled in a case about one of Arkansas’s other execution drugs, and Monday’s other developments added to this state’s complex and high-profile history with the death penalty. As a presidential candidate and Arkansas governor in 1992, Bill Clinton left the campaign trail to preside over an execution.

Later, in 1994, Arkansas was the site of the nation’s first triple execution in 32 years. Arkansas has repeatedly conducted double executions, and in 2015, a poll commissioned by the University of Arkansas showed overwhelming support for capital punishment here.

But Governor Hutchinson set off an international furor when, in February, he scheduled eight executions that were to take place over less than two weeks in April. The schedule, death penalty researchers and historians said, was unequaled in the modern history of capital punishment in the United States, which reinstated the death penalty in 1976.

Mr. Hutchinson suggested he had little choice: Arkansas’s midazolam supply will expire at the end of this month, and the authorities did not believe they would be able to restock it easily.

Although the schedule narrowed as judges issued stays of execution, Mr. Hutchinson faced pressure to back away from his plans, and the Governor’s Mansion in Little Rock was the scene of protests.

“What Governor Hutchinson is faced with is really an extraordinary situation,” said Jim Guy Tucker, who, as a Democratic governor of Arkansas in the 1990s, oversaw seven executions. “I can’t put myself in his shoes, but I’m profoundly grateful that I was never confronted with that problem.”

Adam Liptak contributed reporting from Washington.