He was a younger son of Madeleine Coustant de Belle-Assise (1705–1771) and Claude Nicolas Mottet (1693–1768), a lawyer in Parlement who was an officer in the King's Venery.
Through his brother Louis-Melchior Mottet, he was an uncle of Agathe de Rambaud, the official nurse of the royal children who was in charge of the Dauphin from 1785 to 1792.
As commissioner, he was responsible for all civil administration, including finance, commerce, navigation, police and justice of the colony.
Mottet and his family chose to stay in Pondicherry, fearing being victims of the Reign of Terror in mainland France during the French Revolution.
Mottet was made Commissioner for all French establishments in India and president of the Superior Council in Pondicherry, but for only a few weeks as he retired on 1 January 1817.