When the Revolutionary Tribunal of Paris was created by the National Convention on 10 March 1793, he was appointed its public prosecutor, an office that he filled until 1 August 1794.
His zeal in prosecution earned him the nickname Purveyor to the Guillotine.
On 26 September 1793 Martial Herman was appointed as president of the tribunal
and René-François Dumas as vice president; Coffinhal as one of the judges.

His activity during this time earned him the reputation of one of the most sinister figures of the Revolution.
His office as public prosecutor arguably reflected a need to display the appearance of legality during what was essentially political command, more than a need to establish actual guilt.
Fouquier de Tinville, like Maximilien Robespierre, was known for his ruthless radicalism.

One of the last groups he prosecuted included seven nuns, aged 32–66, of the former convent of Carmelites, living in Paris, plus an eighth nun, of the Convent of the Visitation,
. .
.who were charged with consorting together and scheming to trouble the State by provoking civil war with their fanaticism....Instead of living at peace within the bosom of the Republic, which had provided for their subsistence, and instead of obeying the laws, adopted the idea of residing together in this same house...and of making this house a refuge for refractory priests and counter-revolutionary fanatics, with whom they plotted against the Revolution and against the eternal principles of liberty and equality which are its basis.

 
Apparently the nuns, whom he called criminal assassins, were corrupted by the ex-Jesuit Rousseau de Roseicquet, who led them in a conspiracy to poison minds and subvert the Republic.
 When the judge read this piece of Fouquier-Tinville's prose, he condemned them to be deported, as well as all those who had given them refuge.
When the Revolutionary Tribunal of Paris was created by the National Convention on 10 March 1793, he was appointed its public prosecutor, an office that he filled until 1 August 1794. His zeal in prosecution earned him the nickname Purveyor to the Guillotine. On 26 September 1793 Martial Herman was appointed as president of the tribunal
and René-François Dumas as vice president; Coffinhal as one of the judges.
His activity during this time earned him the reputation of one of the most sinister figures of the Revolution. His office as public prosecutor arguably reflected a need to display the appearance of legality during what was essentially political command, more than a need to establish actual guilt. Fouquier de Tinville, like Maximilien Robespierre, was known for his ruthless radicalism.
One of the last groups he prosecuted included seven nuns, aged 32–66, of the former convent of Carmelites, living in Paris, plus an eighth nun, of the Convent of the Visitation,
. . .who were charged with consorting together and scheming to trouble the State by provoking civil war with their fanaticism....Instead of living at peace within the bosom of the Republic, which had provided for their subsistence, and instead of obeying the laws, adopted the idea of residing together in this same house...and of making this house a refuge for refractory priests and counter-revolutionary fanatics, with whom they plotted against the Revolution and against the eternal principles of liberty and equality which are its basis.
 
Apparently the nuns, whom he called criminal assassins, were corrupted by the ex-Jesuit Rousseau de Roseicquet, who led them in a conspiracy to poison minds and subvert the Republic.  When the judge read this piece of Fouquier-Tinville's prose, he condemned them to be deported, as well as all those who had given them refuge.
Antoine Quentin Fouquier-Tinville