His skills as a draftsman led him to work as project architect on several major archaeological excavations in Mesopotamia and Assyria during the early 1850s.

[2] He was also required to make casts and stampings of inscriptions, using the new and still secret procedure developed by Lattin de Laval.

The excavations, originally started by Paul-Emile Botta in 1843, were languishing, and the French government was determined to mount a large-scale operation in Assyria to showcase its dominance in the region.

Victor Place, the new French Consul in Mosul hired Thomas to join the expedition as the project designer.

[4] Many of the Assyrian antiquities were lost in May 1855 when the expedition's boat sank in the Qurnah Disaster on the Tigris, following an attack by local rebels.

His travels in Italy, Greece, and Turkey and the Middle East inspired his artistic vision and he began painting works in the Orientalist genre.