Officials believe the men are the first in the state to be posthumously pardoned in a capital murder case.
Black landowners Thomas and Meeks Griffin were executed 94 years ago after a jury convicted them of killing 73-year-old John Lewis, a wealthy white veteran living in Blackstock, a Chester County town 40 miles north of Columbia. Two other men were also put to death for the crime.
Joyner learned about his uncles' fate during filming of the PBS documentary "African American Lives 2," which traced his lineage.
The talk show host and legal historian Paul Finkelman then began to work to clear the Griffins' names because they thought they were framed by another man who was linked to the victim's stolen pistol. John "Monk" Stevenson testified against the others in exchange for a life sentence, but later told fellow inmates the four men had nothing to do with the crime and he pointed his finger at them to save himself.
Joyner and his attorney made a presentation to the state parole and probation board on Wednesday, then left the room while the board voted.
Joyner said he waved his hands and hugged family members when he got word of his great uncle's pardons.
"This won't bring them back, but this will bring closure. This is a very good day," he said.
More than 120 people signed a petition asked for a reduced sentence for the men, including Blackstock's mayor, a former sheriff, two trial jurors and the grand jury foreman, but then-Gov. Richard Manning refused clemency or a pardon, sending the men to the death chamber.