Sirmond is known especially for his lifelong feud with
Mathieu de Morgues, known as the lord of Saint-Germain, who favored
Marie de Médicis and was against
Cardinal Richelieu. Jean Sirmond answers it with a series of small works which he writes under various pseudonyms, such as Julius Pomponius Dolabella, the faithful French or Sieur of the Mountains. At the time of his stay in
Paris, Sirmond collaborated in the drafting of the statutes of the l'
Académie française, of which he became one of the first members in 1634. He also authored a
Life of the Cardinal of Amboise, published in 1631, and wrote Latin poems, published posthumously in 1653. After the death of the king and the cardinal, he withdrew to his native
Auvergne, finding himself without support after having fought so much.
Paul Pellisson paid Sirmond a personal homage, which also constitutes a testimony on the evolution of the
French language, which some said was now sufficiently "reasonable" to be worthy to replace Latin and the Greek as the erudite and literary language of the day. Pellison writes: ==Writings==