The body was found in a peat bog - a wetland environment which can aid preservation of organic matter - in the village of Bellaghy after police archaeologists were alerted in October to the presence of human bones on the surface.
Detective Inspector Nikki Deehan said on Thursday police were initially unsure whether the remains were ancient or the result of a more recent death, but radiocarbon dating showed the time of death was between 2,000-2,500 years ago.
Other so-called "bog bodies" - the naturally preserved remains of long-deceased humans found in peat bogs - have been recovered and studied over the years, most commonly from Northern Europe.
"This is the first time radiocarbon dating has been used on a bog body in Northern Ireland, and the only one to still exist, making this a truly unique archaeological discovery for Northern Ireland," Deehan said.
The excavations uncovered a tibia and fibula and a humerus, ulna and radius bone, belonging to the left leg and right arm possibly of a male aged between 13-17 at the time of death, police said, adding little is known so far about how the individual died.
The skeleton also had the presence of partial skin, fingernails, toenails and possibly a kidney.
John Joe O'Boyle, Chief Executive of Northern Ireland's Forest Service, called the discovery a "very exciting find" and said the body would be transferred to the museum service for further examination and preservation.
"It certainly adds an important chapter to the historical and cultural significance of this hinterland and archaeological discoveries of bog bodies across Europe," O'Boyle said.
