Thompson was born at Cranley Place, South Kensington, the eldest of five children of Dr. Reginald Edward Thompson (1834-1912) and Anne Isabella De Morgan,[1] and educated at Colet Court, St Paul's School and Caius College, Cambridge, where he read oriental (Hebrew and Aramaic) languages.

In 1918 Mesopotamia became a possession of the UK, and the trustees of the British Museum applied to have an archaeologist attached to the army in the field to protect antiquities from harm.

As a captain in the Intelligence Service serving in the region and a former assistant of the British Museum, R. C. Thompson was commissioned to start the work.

[1] The writer Agatha Christie and her husband the archaeologist Max Mallowan were invited by Thompson to the excavation site at Nineveh in 1931.

Reginald Perronet was a Flight Lieutenant in the Royal Air Force Reserves (RAFVR), and was killed on active service on 4 April 1941.