A jury in coastal Brunswick took about two hours to decide on a sentence of death for 61-year-old David Edenfield.
They convicted him in the March 2007 sexual assault and choking death of young Christopher Michael Barrios.
The 6-year-old's body was later found wrapped in trash bags and dumped near a road.
Edenfield is the first of three suspects to stand trial for the boy's slaying. His wife and grown son have also been charged in the crime.
Prosecutors said Edenfield "convicted himself" in a taped confession to police.
Defense attorneys had argued that police may have led Edenfield to make a false confession.
Contributors: Rickey Bevington