Leclerc was the son of a civil engineer and joined the National Guard in Clermont-Ferrand at the outbreak of revolution in 1789.
[2] He returned to metropolitan France and joined the 1st battalion of Morbihan in which he served until February 1792, when he left for Paris to defend seventeen grenadiers accused, in Martinique, of being revolutionaries.
On April first that year he made a speech before the Jacobin Club calling for the execution of King Louis XVI and Marie Antoinette.
In 1793, he married Pauline Léon, who together with Claire Lacombe had founded the Société des républicaines révolutionnaires, a radical and revolutionary feminist organization which was banned the following year.
He and his wife published a broadsheet called L'Ami du peuple par Leclerc starting in 1793, which advocated a radical purging of the army, the creation of a revolutionary army made up exclusively of the partisans of the Reign of Terror, and the execution of all the suspected anti-revolutionaries.