He was born in Arras, the youngest of four children of the lawyer Maximilien-Barthelemy-François de Robespierre and Jacqueline-Marguerite Carraut, the daughter of a brewer. His mother died when he was one year old, and his grief-stricken father abandoned the family to go to Bavaria, where he died in 1777. He was brought up by an aunt and trained as a lawyer. His brother Maximilien had won a scholarship from the Abbey of St. Vaast to pay for his studies at the Lycée Louis-le-Grand and had been such an outstanding student that when he obtained his degree in law, he asked the Abbot, Cardinal de Rohan, if he would transfer the scholarship to Augustin to allow him to follow the same career. The Cardinal agreed and Augustin took up his brother's place studying law.
Although his political views were very similar to those of his brother, Augustin was very different in character. Handsome, he was also fond of good food, gaming and the company of women. At the outset of the Revolution, Augustin was prosecutor-syndic of Arras. He founded a political club in the town and wrote to his brother to secure its affiliation with the Jacobins in Paris. In 1791, he was appointed Administrator of the département of Pas-de-Calais.
Augustin unsuccessfully stood for election to the new Legislative Assembly in Arras in August 1791, but his views were too radical for the town, which elected another young lawyer, Sixte François Deusy instead. However on 16 September 1792, Augustin was elected to the National Convention,19th out of 24 deputies, with 392 votes out of 700 cast, by the voters of Paris, and he joined his brother in The Mountain and the Jacobin Club. At the Convention he distinguished himself by the vehemence of his attacks on the royal family and on aristocrats. During the trial of Louis XVI he voted for the death penalty to be applied within 24 hours.
When he first came to Paris to take his seat he was accompanied by his sister Charlotte, and they both lodged with Maximilien in the house of Maurice Duplay. Soon however Charlotte persuaded Maximilien to come with them to a new lodging in the rue Saint-Florentin where she could look after he two brothers. He soon returned to the Duplay's house however, leaving Augustin and Charlotte to live by themselves. However this arrangement did not last long either. In August 1793 Augustin was sent on a mission to Alpes-Maritimes to suppress the Federalist revolt, together with another deputy from the Convention, Jean François Ricord, and Charlotte accompanied him. Much of southeastern France was in rebellion against the Republic, and they barely made it alive to Nice after a very dangerous journey. In Nice they felt secure enough to attend the theatre, but on the third occasion they did so, they were pelted with rotten apples. In 19 December 1793 Augustin took part in the military action, led by Dugommier and Napoleon, which retook Toulon from the British. On their return to Paris, Augustin moved out of the lodging with Charlotte and went to live with Ricord and his wife.
In 1794 Augustin was dispatched once again as a representant en mission, now to the Army of Italy in Haute-Saône. This time he took with him not his sister but his mistress, La Saudraye, the creole wife of a literary man. He used his influence to advance Napoleon Bonaparte's career, after reading Napoleon's pro-Jacobin pamphlet titled Le souper de Beaucaire. On his return to Paris he served a secretary to the Convention.
Augustin was with his brother in the chamber of the Convention on the evening of 9 Thermidor (27 July 1794), when the deputies voted for the arrest of Robespierre. At once, Augustin rose from his place on the benches and said "I am as guilty as him; I share his virtues, I want to share his fate. I ask also to be charged". He was promptly arrested too, along with Saint-Just, Couthon and Lebas. Hearing of the arrests, the Commune of Paris issued orders to all prisons in the city, forbidding them to take the prisoners in. For this reason they were kept under guard in the rooms of the Committee of General Security, where they remained until a place could be found for them. Eventually Augustin was held in the prison of La Force while Maximilien was held in the Luxembourg. Because of the Commune's orders however, they were soon released and made their way to the Hôtel de Ville here they spent the night vainly trying to coordinate an insurrection. On the morning of 10 Thermidor, the forces of the Convention under Barras burst in and succeeded in taking most of them alive.
Augustin escaped through one of the windows of the Hôtel de Ville, and threw himself head first onto the steps of the grand stairway. He was picked up, still alive, and taken away with his brother. He declared that neither he nor his brother had, for one instant, fallen short in their duty to the Convention. Barras ordered him to be taken, in whatever state he was, back to the rooms of the Committee of General Security. From there the prisoners were taken to the Conciergerie prison, and after a summary trial at the Revolutionary Tribunal, they were sent to their deaths. Couthon was the first of the prisoners executed, with Augustin second. Maximilien was the last but one.