In 1733, aged 15, he took part in his first campaign as an aid in the staff of Marshal Louis de Noailles, who was his uncle.

He also grew interested in natural history, chemistry, geography, physics, mechanics and astronomy.

He gave his son, Charles François César Le Tellier, a thorough education, which earned him an honorary seat at the Academy of Sciences.

Le Tellier had a ship build, Aurore, which he used to test the various candidates in real conditions at sea.

The expedition also comprised Pingré, Messier and the watchmaker Le Roy, who had built two of the chronometers.