The lion figurine, made from ivory, dates back to the Ice Age and was found in 1931 during excavations in the Vogelherd Cave in southwestern Germany.
But since the find, it has only had half its head - until now.
Archaeologists from the University of Tübingen found an ancient fragment which makes up the missing side of its head.
Professor Nicholas Conard from the university said: “It is one of the most famous Ice Age works of art, and until now, we thought it was a relief, unique among these finds dating to the dawn of figurative art.
“The reconstructed figurine clearly is a three-dimensional sculpture.”
The new fragment was discovered when archaeologists revisited the work of their predecessors from the 1930s.
“We have been carrying out renewed excavations and analysis at Vogelherd Cave for nearly ten years,” said Conard. “The site has yielded a wealth of objects that illuminate the development of early symbolic artifacts dating to the period when modern humans arrived in Europe and displaced the indigenous Neanderthals.”
The Vogelherd Cave, just north of Ulm in Baden-Württemberg, has provided evidence of the world’s earliest art and music and is a key element in the push to make the caves of the Swabian Jura region a Unesco World Heritage site.
It is one of four caves in the region where the world’s earliest figurines have been found, dating back to the Upper Paleolithic era.
Several dozen figurines and fragments of figurines have been found in the Vogelherd alone and researchers are piecing together thousands of mammoth ivory fragments.
The new-look lion can be seen at the University Museum in Hohentübingen Castle.