King in Prussia
In 1687 Ancillon was appointed head of the so-called "Academie des nobles," the principal educational establishment of the state; later on, as councillor of embassy, he took part in the negotiations which led to the assumption of the title of "King in Prussia" by the elector. In 1699 he succeeded Samuel Pufendorf as historiographer to the elector, and the same year replaced his uncle Joseph Ancillon as judge of all the French refugees in the Margraviate of Brandenburg.