On the death of his elder brother, Louis IV Chauvelin, in 1715, he added the officer of avocat général to the parlement de Paris then, in 1718, bought a post as président à mortier, raising him to the top of the judicial hierarchy.
Chauvelin became Fleury's collaborator and advisor and when Fleury became prime minister in 1726 he was quick to bring Chauvelin into his cabinet, making him garde des sceaux on 17 August 1727 following the dismissal of Joseph Fleuriau d'Armenonville, then secretary of state for foreign affairs the following day after the dismissal of Charles Jean Baptiste Fleuriau de Morville.
As Garde des sceaux, Chauvelin had to share his powers with Henri François d'Aguesseau, who held onto the unsackable post of Chancellor of France.
In 1734, he became 'seigneur engagiste' of the Château de Brie-Comte-Robert, and in 1750 razed its towers and courtyards down to a single storey, sparing the tour Saint-Jean, the seigneurial symbol.
He was able to return to Paris in April 1746 thanks to the intercession of marquis d’Argenson and the comte de Maurepas but stayed out of political life from that date until his death in 1762.