Desmoulins was born at Guise, Aisne, in Picardy. His father was lieutenant general of the bailliage of Guise, and through the efforts of a friend obtained a scholarship for his son at the Collège Louis-le-Grand in Paris. In addition to his government post Desmoulins' father was also a local lawyer to the residents of the countryside. Entering the school, which Maximilien Robespierre and Louis-Marie Stanislas Fréron also attended at the time, at fourteen, Desmoulins was an accomplished student. It is here that his love for the classics, such as Cicero, Tacitus and Livy would prosper. Destined by his father for the law, he was admitted as a lawyer of the parlement of Paris in 1785. However, he did not do well, as he had a violent manner and a serious stammer. This prompted him to turn towards writing. His interest in public affairs led him to a career in politics.

In March 1789, Desmoulins was nominated deputy from the bailliage of Guise. He came to Laon as a commissioner for the election of deputies to the Estates-General. As a spectator of the procession of the Three Estates on May 5, 1789, Desmoulins wrote a response, an Ode aux Etats Generaux and later Mirabeau enlisted him to write for his newspaper, although it was ephemeral, for it was banned by royal decree on May 6, 1789.

Because of his failure as a lawyer, he lived in extreme poverty in Paris. However, he was enthusiastic about the political changes heralded by the summoning of the Estates-General. In his letters to his father, he rhapsodizes over the procession of deputies entering the Palace of Versailles, and criticizes the events following the closing of the Salle des Menus Plaisirs to the deputies who had named themselves the National Assembly - leading to the Tennis Court Oath.

The sudden dismissal of Jacques Necker by King Louis XVI brought fame to Desmoulins. On July 12, 1789 he leapt on a table outside one of the cafés in the garden of the Palais Royal, and announced to the crowd the dismissal of the reformer. Apparently losing his stammer due to the excitement, he addressed the passions of the public, calling them to "... take up arms and adopt cockades by which we may know each other" and adding: "This dismissal is the tocsin of the St. Bartholomew of the patriots!", claiming that a massacre of the partisans of reform was under preparation. He adopted green as the color for rallying liberty and the masses followed, for he had become their leader. Finally, after drawing two pistols from under his coat, he declared that he would not fall alive into the hands of the police who were watching his movements. He descended, embraced by the crowd.

Following Desmoulins, riots started throughout Paris. The mob, procuring arms by force on July 13, was partly organized as the Parisian militia, which was afterwards to be the National Guard. On July 14, the storming of the Bastille occurred.

The following day, Desmoulins began the most publicised phase of his writing career. In May and June 1789 he had written La France Libre, which his publisher had refused to print. The taking of the Bastille, however, was a sign of changing times, and, on July 18, Desmoulins's work was issued. Considerably in advance of public opinion, it called explicitly for a republic, his sixth issue stating, "... popular and democratic government is the only constitution which suits France, and all those who are worthy of the name of men." "La France Libre" also elaborately examined the rights of king, of nobles, of Roman Catholic clergy and of the people, it became instantly popular, securing Desmoulins a partnership with Honoré Mirabeau. It was immediately followed by a slander campaign from Royalist pamphleteers.

Desmoulins was a member of the Cordelier Club, a revolutionary political club filled with outright supporters of a French republic. During his entire career Desmoulins believed that a republic was necessary to save France. In addition to his involvement in the Cordelier Club, he also frequented the Jacobin Club, which at this point contained a range of political opinions, from those who supported a constitutional monarchy to more radical republicans. Desmoulins looked back to the early Greek and Roman Republics and argued, in a more radical fashion than many, that the nation should model a new French Republic after these historic precedents.

Exhilarated, he appealed to the lower orders by printing his Discours de la lanterne aux Parisiens which began with a quotation from the Gospel of John, Qui male agit odit lucem ("He that does evil hates light" John 3:20). This example of gallows humour alludes to the use by rioters of the iron bracket of a lantern at the corner of the Rue de Grève and the Rue de la Vannerie as a makeshift gallows to hang suspected spies and profiteers. A famous Revolutionary song the "Ça ira" ("It shall be") includes the lines "Les aristocrates a la lanterne. On les pendra" ("Take the aristocrats to the lantern and hang them"). As a result of the pamphlet, Desmoulins was dubbed "Procureur-général de la lanterne" ("The Lanterne Prosecutor"). In this pamphlet, he argued that revolutionary violence was justified.

In November 1789, he began a career as a journalist with the first number of a weekly publication, Histoire des Révolutions de France et de Brabant, which ceased at the end of July 1791. The publication was extremely popular from its first to its last number - Desmoulins became famous and was no longer poor. The Histoire des Révolutions is a measure of the ideas in circulation in revolutionary Paris, but it has drawn criticism for its extremely violent tone. It was in "Revolutions de France et de Brabant" that scholars begin noting Desmoulins as a “volatile” writer. As the Revolution progressed the French government suffered a great shortage of money and the country entered inflation, Desmoulins did not portray it in this light, however, and “painted a wholly erroneous picture of the situation.” Desmoulins's friendship with important figures, such as Mirabeau and Malouet, suffered from his actions. Both men, fed up with his publishing and libels declared that Desmoulins should be denounced and Malouet, “went so far as to ask that Camille be certified insane.” Robespierre came to Desmoulins's rescue, defending his childhood friend and preventing his arrest.

Desmoulins was influenced by the theorists of the Revolution - for some time before the death of Mirabeau in April 1791, he had begun his collaboration with Georges Danton (his associate for the rest of their lives). In July 1791, he appeared before the Paris Commune — the local government of Paris — as head of a group petitioning to depose the king. At the time, under the constitutional monarchy, such a request was treason. The gesture enhanced agitation in the city, and the frequent attacks to which Desmoulins had often been subject were followed by a warrant for the arrest of himself and Danton.

Danton briefly left Paris, while Desmoulins chose to remain and even to make occasional appearances at the Jacobin Club. Upon the failure of this attempt to arrest him, Desmoulins published a pamphlet, Jean Pierre Brissot démasqué, which contained violent attacks. It originated in a conflict between the two, and was followed in 1793 by a Fragment de l'histoire secrète de la Révolution (more usually known by the name Histoire des Brissotins), in which the Girondists, and especially Brissot, were subjected to a populist attack.

Desmoulins published this in response to Brissot calling for the dissolution of the Paris Commune and the Jacobins. It violently attacked the Girondists and Brissot as enemies of the Revolution, resulting in many being arrested and guillotined and in the defacement of Brissot’s career. Desmoulins later regretted writing this. This pamphlet illustrates the constant shift in opinions and friendship of those in the Revolution, because Brissot many times had defended the journals of Desmoulins when he was threatened, almost acting “as a father guiding his son.” Brissot once warned Desmoulins and said, “’You are young Camille Desmoulins, candor is on your lips ... but you are often fooled by that very candor.’”

In late 1793 Desmoulins published Vieux Cordelier which had a massive effect on French politics. In Vieux Cordelier, Desmoulins called for a movement back to the ideas and ideals of the old Cordelier Club. In addition to wanting to bring back old Cordelier ideas, Desmoulins also used his new publication to attack those who were still supporting the outrageous violence that was happening in the Revolution, while Desmoulins still pushed for a Republic he was against the unnecessary violence and bloodshed that had been the trademark of the revolution thus far.

Desmoulins took an active part in the August 10 attack on the Tuileries Palace. Immediately afterwards, as the Legislative Assembly (France) crumbled and various factions and bodies contended for effective power over the country, he became secretary to Danton in the latter's role as the new Justice Minister. On September 8, he was elected a deputy for Paris to the new National Convention, where he remained largely in the background, remaining better known as a journalist. He was affiliated with The Mountain, and voted for the Republic and the execution of the king. Desmoulins became close to Robespierre, and the Fragment de l'histoire secrète de la Révolution was very likely inspired by the latter. The success of the pamphlet did much to install the Reign of Terror and condemn the Girondin leaders to the guillotine. This proved alarming to both Danton and its author.

In December 1793 the first number of the Vieux Cordelier was issued. At first it was directed against the Hébertists and their mission for dechristianization and received Robespierre's approval, but the third number supported Danton's idea of a Committee of clemency, which earned them Robespierre's epithet les indulgents. This caused Robespierre to turn against Desmoulins, who took advantage of the popular indignation roused against the Hébertists to send them to death. Robespierre and Louis de Saint-Just then turned their attention to both the enragés (Jacques Roux's faction) and the indulgents. On January 7, 1794, Robespierre, who on a former occasion had defended Danton and Desmoulins in the National Convention, urged the burning of certain numbers of the Vieux Cordelier in a speech at the Jacobin Club (though he did not at this time condemn Desmoulins or Danton as individuals). Desmoulins replied using a quote from Jean-Jacques Rousseau (who was widely perceived as the intellectual authority for all revolutionary gestures): "burning is not answering". The implied insult led to a bitter conflict. By the end of March, the Hébertists had been guillotined, while Danton, Desmoulins and other leaders of the moderates were placed under arrest.

On March 31, the arrest warrant was signed and executed, and on the 3rd, 4th and 5 April the trial took place before the Revolutionary Tribunal. On being asked his age, Desmoulins replied:

"I am thirty-three, the age of the "sans-culotte" Jesus, a critical age for every patriot" (he was in fact thirty-four).

While awaiting his trial and execution, Desmoulins wrote love letters to his wife, not knowing that she had been arrested and that these letters would never be received. He only learned of his wife's arrest on his way to his own execution, and as he was being led to the guillotine he fought and resisted his captors crying out to his wife, reciting passages from the letters that he had written to her. The accused were prevented from defending themselves by a decree of the Convention. This, together with the false report of a spy (who charged Desmoulins' wife with conspiring in her husband's escape and plotting the "ruin of the Republic"), obtained for prosecutor Antoine Quentin Fouquier-Tinville a death sentence after threatening the jury. The verdict was passed in the accused's absence, and their execution was scheduled for the same day.

Of the group of fifteen guillotined together (also including Marie Jean Hérault de Séchelles, François Joseph Westermann and Pierre Philippeaux), Desmoulins died third, and Danton last.

On December 29, 1790 Desmoulins married Lucile Duplessis, and among the witnesses were Brissot, Jérôme Pétion de Villeneuve and Robespierre. Their only child, Horace Camille, was born on July 6, 1792. Horace was pensioned by the French government, and died in Haiti in 1825. Lucile was arrested a few days after her husband, and condemned to the guillotine on the basis of false charges. She displayed coolness and courage on the day of her death (April 13, 1794).

Desmoulins's most lasting influence over the French Revolution and the Terror lay first in his denunciation of Brissot and the Girondists, and second in the publication of his newspaper Le Vieux Cordelier, which sought to arrest the progress of the Terror by appealing to the earlier ideals of the Revolution and the Cordeliers Club in its less radical days. Desmoulins, as a significant journalist, illustrated the revolutionary power of newspapers freed from censorship and how effectively they could mould the passions of the people, especially the Parisian sans-culottes. He demonstrated the power that newspapers and political journals had over the Parisian populace during times of crisis, but in the final duel with journalists more radical than he, even his influence was overturned. Through the course of his revolutionary political career it is possible to see the radicalization of the revolution and the nature of the Terror as group after group were denounced and even a formerly unquestionable revolutionary patriot like Desmoulins could be denounced as a threat to the goals of the Revolution and sent to the guillotine.