Cassini de Thury was born in Thury - sous - Clermont (Oise), the second son of Jacques Cassini and Suzanne Françoise Charpentier de Charmois. He was a grandson of Giovanni Domenico Cassini, and would become the father of Jean - Dominique Cassini, Conte de Cassini.

In 1735, he became a member of the French Academy of Sciences as a supernumerary adjunct astronomer, in 1741 as an adjunct astronomer, and in 1745 as a full member astronomer. In January, 1751 he was elected a Fellow of the Royal Society.

He succeeded to his father’s official position in 1756 and continued the hereditary surveying operations. In 1744, he began the construction of a great topographical map of France, 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.

His chief works are: La méridienne de l’Observatoire Royal de Paris (1744), Description géometrique de la terre (1775), and Description géometrique de la France (1784), which was completed by his son.

César-François Cassini de Thury died of smallpox in Paris on 4 September 1784,