[3] Cassini de Thury succeeded his father's official position in 1756 and continued the hereditary surveying operations.

[4] In 1744, he began the construction of a great topographical map of France,[5] one of the landmarks in the history of cartography.

The post of director of the Paris Observatory was created for his benefit in 1771 when the establishment ceased to be a dependency of the French Academy of Sciences.

[5] A letter and proposal sent by Cassini de Thury to the Royal Society in London instigated the Anglo-French Survey (1784–1790), which measured the precise distance and direction between the Paris Observatory and the Royal Observatory, Greenwich, by way of a trigonometric survey.

[5] César-François Cassini de Thury died of smallpox in Paris on 4 September 1784.