Rise to power
Saint-Just was born in Decize in 1767. Following the outbreak of the revolution in 1789, Saint-Just soon sided with it, and was elected to the Legislative Assembly in 1791. He also addressed the National Convention a short time before the trial of Louis XVI, stating "A king must reign or die".
By taking the position that Louis should be sentenced to death, Saint-Just was the first to voice a popular opinion that few dared to admit to. Saint-Just was strongly applauded by the Convention and soon became a noted revolutionary figure among the Jacobins.
In September 1793, the Reign of Terror began after the Committee of Public Safety became increasingly powerful. Saint-Just led the Committee along with Maximilien de Robespierre, Georges Couthon, and Jean-Marie Collot d'Herbois, and became a critic of Georges Danton, whom he regarded as too moderate.
Member of the Committee of Public Safety
During his tenure on the Committee, Saint-Just attempted to have the Marquis de Sade imprisoned, believing him to be an immoral influence on the citizens of the French Republic. To accomplish this, he sent an agent to plan the murder of one of de Sade's prostitutes, Suzanna, which the Marquis would be framed for.
De Sade's valet Olivier had come to hate his employer, and the agent took advantage of this, paying Olivier to murder Suzanna, as Saint-Just did not want the Committee to became suspicious. However, the Assassin Arno Dorian investigated the murder, discovered the plot to frame de Sade and had Olivier imprisoned.
Along with Robespierre, Saint-Just also plotted to end the career of Napoleon Bonaparte, a rising captain in the revolutionary army. To accomplish this, Saint-Just deceived several workshops in Paris into using defective materials in their production of military armamants, which would then be delivered to Bonaparte's troops. However, Arno learned of this plot and sabotaged the weapons, thus halting their delivery and protecting Bonaparte's career from Saint-Just and Robespierre's plotting.
Downfall and death
In early 1794, Saint-Just served as the President of the National Convention, and was noted for his unusual waistcoat and long hair. Possibly due to his extreme political positions, a legend grew alluding that Saint-Just's coat was made from human skin in the tanneries of Paris.
These rumors caught the attention of Arno, who was charged by Saint-Just's valet with speaking to a tailor. The valet had ordered a coat for Saint-Just from the tailor, but the tailor refused to deliver it, as he was suspicious about the leather that had been provided. After learning that the coat was indeed made of human skin and that the valet was well aware of this, the Assassin killed him and reported this to the tailor, who promised to use the leather as evidence in order to bring down Saint-Just.