Brandon Jones, scheduled to receive a lethal injection at a state prison in Jackson, has spent more than 36 years behind bars for the 1979 murder of a convenience store clerk.
Critics point to his case as an example of the "double punishment" faced by some death row prisoners -- spending decades in solitary confinement with no prospects but death.
Supreme Court Justice Stephen Breyer last year spoke out against "unconscionably long delays that undermine the death penalty's penological purpose."
"Jones's case raises questions of proportionality and discriminatory application of the death penalty," the Death Penalty Information Center said in a statement.
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"He and his co-defendant Van Solomon -- both African American -- were sentenced to death... For killing a white gas station store clerk during a robbery.
"Jones denies shooting the clerk and prosecutors never determined who fired the fatal shot."
Solomon died on the electric chair in 1985.
During the decades he spent behind bars, Jones read a lot and become known for his writings on prison life and issues of race.
Jones, who would turn 73 on Valentine's Day, declined to request a final meal ahead of his 7:00 pm (local time) execution.
"He will be receiving the institutional tray consisting of chicken and rice, rutabagas, seasoned turnip greens, dry white beans, cornbread, bread pudding and fruit punch," the Department of Corrections said in a statement.
Jones would be the fifth person executed in the United States this year.