The governor of Oklahoma on Thursday called off the execution of a death-row inmate just hours before the man was to be put to death, in a case in which the state’s Pardon and Parole Board had twice recommended that his sentence be commuted.

“After prayerful consideration and reviewing materials presented by all sides of this case, I have determined to commute Julius Jones’s sentence to life imprisonment without the possibility of parole,” Gov. Kevin Stitt said in a statement.

The man, Julius Jones, was convicted of first-degree murder and sentenced to death in 2002. He was found guilty of killing Paul Howell, who was in a car in the driveway of his parents’ home when he was carjacked and fatally shot in 1999. The commutation came less than a month after the Supreme Court, with its three more liberal members dissenting, lifted a stay of execution that a federal appeals court had granted to Mr. Jones and another Oklahoma death row inmate, John Marion Grant, who was executed last month.

Mr. Jones, 41, a former high school basketball player from Oklahoma City, was 19 at the time of the killing, which he says he did not commit. Mr. Howell, a businessman from the suburb of Edmond, was 45.

Hundreds of students had walked out of schools and activists demonstrated outside Mr. Stitt’s office this week in an attempt to persuade him to spare Mr. Jones.

In a statement, Amanda Bass, a lawyer for Mr. Jones, said that Mr. Stitt’s decision would restore “public faith in the criminal justice system.”

“While we had hoped the governor would adopt the Board’s recommendation in full by commuting Julius’s sentence to life with the possibility of parole in light of the overwhelming evidence of Julius’s innocence, we are grateful that the governor has prevented an irreparable mistake,” she said.

Protesters who had gathered at the State Capitol erupted in cheers after Mr. Stitt’s statement was released.

Mr. Stitt’s announcement came soon after federal public defenders filed an emergency motion asking a federal judge to stay the execution based on “compelling evidence” that the drugs used in lethal injections “pose a serious and substantial risk of severe suffering and pain to prisoners.” Last month, a death-row inmate in Oklahoma vomited and shook during an execution.

The motion urged the court to grant an injunction to ensure that Mr. Jones and three other death-row inmates were not executed before February, when a federal trial is set to begin in a long-running lawsuit over whether the drugs used in executions risk subjecting inmates to an unconstitutional amount of pain and suffering.

In September and again this month, the state’s Pardon and Parole Board recommended that Mr. Jones’s sentence be commuted to life in prison with the possibility of parole, a significant step in a case that has garnered national attention, said Cece Jones-Davis, who directs an Oklahoma-based campaign called Justice for Julius.

In the days and hours before Mr. Jones’s planned execution, scheduled for 4 p.m. local time on Thursday, his family and his supporters waited to hear whether Mr. Stitt, a Republican, would accept or reject the board’s recommendation, Ms. Jones-Davis said.

The Oklahoma City Public Schools estimated that more than 1,800 students across 13 schools participated in walkouts to support Mr. Jones on Wednesday. The district said it “supports our students’ rights to peaceful assembly and their freedom of expression.”

At the State House, scores of Mr. Jones’s supporters prayed, sang and chanted “free Julius Jones.” Madeline Davis-Jones, Mr. Jones’s mother, told the crowd that her son was innocent.

“If my child is executed tomorrow, or any day, it should be without a doubt,” she said. “It shouldn’t be a doubt. Not even a little bit of doubt.”

If he had been executed, Mr. Jones would have been the second person put to death this year by the State of Oklahoma. Mr. Grant, who was convicted of murdering a prison cafeteria worker in 1998, was executed on Oct. 28, hours after the stays were lifted.

Mr. Grant, 60, was the state’s first to die by lethal injection since 2015, when Oklahoma stopped executions after using the wrong drug in one instance and allowing a prisoner to regain consciousness in another. Mr. Grant and Mr. Jones had argued that the state’s lethal injection protocol, which uses three chemicals, could subject them to excruciating pain.

Mr. Grant vomited while shaking for several minutes during the execution, which reporters who have witnessed executions called extremely rare in their experience. But state prison officials said a day after Mr. Grant’s execution that they did not plan to make any changes to the state’s lethal injection protocols.

“I will agree inmate Grant’s regurgitation was not pleasant to watch,” Scott Crow, the director of Oklahoma’s prison system, said at a virtual news conference on Oct. 29. “But I do not believe that it was inhumane.”

Mr. Jones, a Black man who has spent about half of his life in prison, has long maintained his innocence.

“I did not kill Mr. Howell,” he wrote in a letter to the parole board in April, after he had exhausted his appeals. “I did not participate in any way in his murder; and the first time I saw him was on television when his death was reported.”

But relatives of Mr. Howell, a white man whose sister and two daughters witnessed his killing, have rejected those claims and said that the efforts to grant clemency to Mr. Jones have caused them pain.

“Our family continues to be victimized by Julius Jones and his lies,” Mr. Howell’s brother, Brian Howell, said at a news conference in September.

Mr. Jones and his supporters have argued that his defense lawyers failed him during his trial — for instance, by neglecting to question family members who have said that he was having dinner with them at the time of Mr. Howell’s killing — and that prosecutors relied too heavily on the testimony of a co-defendant who said that he had seen Mr. Jones commit the crime.

Mr. Jones’s supporters have also argued that racism played a role in his trial and sentencing. African Americans make up a disproportionate number of death row prisoners in Oklahoma and in the United States, and research has shown that people convicted of murder are much more likely to be executed if the person who was killed was white.

Mr. Jones’s appeal for clemency drew support from prominent figures in sports, politics and entertainment.

Last month, Matt Schlapp, the chairman of the American Conservative Union, and Timothy Head, the executive director for the Faith & Freedom Coalition, wrote a letter to Mr. Stitt urging him to commute Mr. Jones’s sentence.

“We believe that doubt about Jones’s responsibility for the capital crime is not insignificant,” Mr. Schlapp and Mr. Head wrote.

Mr. Jones’s case has been featured in a 2018 documentary series produced by Viola Davis, a podcast episode last year featuring Kim Kardashian West and a recent episode of “The Late Late Show With James Corden.”

“Julius, his family and everyone on his team are still hopeful Stitt will do the right thing,” Ms. Kardashian West wrote on Twitter on Tuesday.

Jacey Fortin contributed reporting.