A doctor of theology, he was 'garde' of the king's library and entered the Académie française aged 29.
He translated the Rhetorica (then thought to be by Cicero) and Sallust's Histories from Latin into French - Chapelain stated that Cassagne wrote "[in a] more natural than acquired [style], especially in the field of human letters[1]".
Also a renowned preacher, he was cruelly mocked by Boileau in the latter's third Satire, referring to people squashed in to listen to the "sermons of Cassaigne" and those of Charles Cotin.
In 1668, he published a poem Sur la conqueste de la Franche-Comté (On the conquest of the Franche-Comté, during the War of Devolution) and in 1672 a Poëme sur la guerre de Hollande (Poem on the war with Holland, referring to the Franco-Dutch War).
Boileau commented on these poems: With failing health, Cassagne died aged only 46, possibly due (some said) to the grief this satire had caused.