He falsely claimed to be a descendant of La Fontaine by his mother and Racine by his father.
In 1786, he published the first part of Lettres à Emilie sur la mythologie.
These works, alternating prose and madrigal-like verses, were very successful.
Demoustier tried to edit Lettres à Emilie sur la mythologie, but the bookseller who owned the copyrights refused to let him do so, perhaps because he had a stock of earlier copies he wanted to get rid of first.
Demoustier was unable to wait, as he died a painful, premature death, in Paris, soon after.