Corday was a Girondin sympathizer who came from an impoverished royalist family; her brothers were émigrés who had left to join the exiled royal princes.

From her own account, & those of witnesses, it is clear that she had been inspired by Girondin speeches to a hatred of the Montagnards & their excesses, symbolised most powerfully in the character of Marat. The Book of Days claims the motive was to "avenge the death of her friend Barboroux".

Marat's assassination contributed to the mounting suspicion which fed the Terror during which thousands of the Jacobins' adversaries – both royalists & Girondins – were executed on charges of treason. Charlotte Corday was guillotined on 17 July 1793 for the murder. During her four-day trial, she testified that she had carried out the assassination alone, saying "I killed one man to save 100,000."