Officials at the Getty said in a release on Monday that the museum acquired the manuscript in 1983 as part of a "large, well-documented" collection.
The manuscript is currently at the Getty Center in Brentwood as part of the exhibition "Heaven and Earth: Byzantine Illumination at the Cultural Crossroad." It has been featured in 14 exhibitions at the Getty, and was loaned to New York's
The Getty said it conducted research into the manuscript with the Hellenic Ministry of Culture and Sports over the last six weeks.
"Based on new information that came to light through this process, the museum decided that the right course of action was to return the manuscript to the Holy Monastery of Dionysiou from which it disappeared over 50 years ago," said Timothy Potts, director of Getty Museum, in a statement.
The Getty said the research yielded a 1960 monastery record indicating that the book had been illegally removed. The museum said the report of its disappearance had never been made public, nor had information about the theft been made available to the Getty, to law enforcement officials or to any databases of stolen art.
In 2011, the Getty signed a memorandum of understanding with Greece under which both parties agreed to deter the illicit traffic in antiquities. The agreement also provided for cultural exchanges and joint scientific research.
The agreement stems in part from the museum's past troubles with Greece and Italy over looted antiquities. The disputes centered in large part on former Getty antiquities curator Marion True, who was accused of purchasing illegally excavated items.
The Getty said the New Testament manuscript will be returned to Greece after the "Heaven and Earth" exhibition closes in June 22. The Getty Villa will host the companion exhibition "Heaven and Earth: Art of Byzantium from Greek Collections" beginning Wednesday and running until Aug. 25.