Along with the Crimson Rose, de Choisy opposed the Revolution and was a member of the former's Crimson League, dedicated to protecting Templar aristocrats from the guillotine. Described by the Crimson Rose as an honorable man, de Choisy believed himself to be better than the lower class revolutionaries.
During the Revolution, he was arrested and sentenced to be guillotined. Occupied with other matters, the Crimson Rose sent the Assassin Arno Dorian to rescue him, neither of them being aware of each other's true allegiance. After searching de Choisy's house, Arno found him near the Church of Saint Gervais. While belittling his captors and claiming that the Crimson Rose would save him, de Choisy was freed by Arno, although the Templar complained that he had not done so sooner.
Arno soon learned from the Chevalier d'Éon that the Crimson League consisted of Templars. As de Choisy and his fellow Templars planned to flee to England, Arno found them at the docks near the Pont Marie. De Choisy showed impatience, wishing to dine with his cousin Percy in England. Arno then assassinated the Templars at the docks, before assassinating the Crimson Rose himself.
- De Choisy's cousin, Lord Percy, is a reference to Sir Percy Blakeney, the protagonist of the novel The Scarlet Pimpernel.