Born at Riom (Puy-de-Dôme), the son of a wealthy family of merchants, Pierre (as he is usually called) Chanut made a career in administration (tax and finance). Alongside his official duties he also worked with Marin Mersenne and Pierre Petit (1598–1677) on scientific questions, especially the barometric experiments. In the 1640s, he entered the foreign service and before long became one of France's top diplomats, more particularly in charge of the relations with Northern Europe. After traveling extensively in Sweden, Northern Germany, and the United Provinces, he returned definitively to France in 1655. Being a trusted client of Fouquet (1615–80), Chanut retired from the public service when the latter fell into disgrace (1661).

The first time Descartes mentions Chanut is in mid-March 1642 in connection with the objections of Pierre Bourdin (AT III 546). Meetings probably followed during Descartes’ journey to France in 1644 because in 1645 Descartes already refers to Chanut as “one of my best friends” (AT IV 300). They also met at Amsterdam, when Chanut's ship made a stop on its way to Sweden (Baillet 1691, II 279). It is through Chanut that Claude Clerselier entered the Cartesian orbit, Chanut being married (1626) to Clerselier's sister Marguerite. On arriving in Sweden, Chanut tried to interest Queen Christina in Descartes. His motives were primarily political, Descartes being an asset in his attempts to consolidate the relations with Sweden after the Thirty Years’ War (1618–48) would be over. Chanut showed some of Descartes’ letters to her (AT V 59), and by December 1646 another senior diplomat had already visited Descartes to sound him on a formal invitation (AT IV 535–36, CSMK 298–99). Although initially Descartes’ reaction had been hesitant, he yielded after Chanut, on behalf of Queen Christina, asked his opinion on the sovereign good in the autumn of 1647 (AT V 81–86, CSMK 324–26). Descartes was formally invited in February 1649; he left the United Provinces in the autumn of 1649 and arrived in Sweden in September.