Théodule Devéria help Mariette read inscriptions in Cairo and its surroundings. He tried to accurately document the archaeological sites using drawings, stampings and photographs. His calotype pictures from this trip are often poor in quality, showing a lack of technical skills. In 1860 he was appointed preserving assistant at the Louvre's Department of Egyptology. He revisited Egypt in 1861–62, traveling up the Nile to Philae at the First Cataract, and into Nubia to the Abu Simbel temples. After returning he helped Mariette prepare descriptions of the excavation in Egypt in 1850–54 for publication. In November 1864 Devéria met the future oriental scholar
Prince Sadruddin Aga Khan Nations Educational, Scientific and Cultural Organization (UNESCO) in 1958, and became the Executive Secretary to its International Action Committee for the Preservation of Nubia in 1961. This initiative brought together archaeologists from Eastern Europe and the West at the height of the Cold War. The construction of the Aswan Dam threatened ancient Egyptian treasures including Abu Simbel, the temples of Philae and Kalabsha, and the Christian churches of Nubia. He would later describe it as "one of UNESCO's great achievements" because of the challenging historical context in which it took place—in particular the ongoing tensions in the Middle East and