He joined the French Royal Army in 1776 and was badly wounded in the American Revolutionary War two years later.

After a short stint in the Royal Marine, Moreaux enlisted in the Auxerrois Grenadier Regiment in 1776 and was sent overseas to fight in the American Revolutionary War.

[1] Between 3 and 5 September 1792, a garrison of 3,000 to 4,000 French soldiers successfully held Thionville against 20,000 Austrians and Émigrés under Friedrich Wilhelm, Fürst zu Hohenlohe-Kirchberg.

Out of 3,000 soldiers, the French lost 103 men and five guns captured plus an unknown number of killed and wounded.

[4] In the Battle of Pirmasens on 14 September, Moreaux was defeated by a Prussian army under Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel.

The name of the French commander of the Corps of the Vosges is spelled "Moreau" in historian Digby Smith's account.

Two months later Jean-Baptiste Jourdan succeeded Hoche in command and the army pulled back to a position between Thionville and Sarrebruck.

[1] On 25 June 1794, Moreaux was named commander of the Army of the Moselle, taking over from Claude Ignace François Michaud.

[11] One of Moreaux's divisions led by Rémy Vincent captured Rheinfels Castle on 2 November leaving only Mainz and Luxembourg City in enemy hands on the Rhine's west bank.

[12] While Michaud's Army of the Rhine received instructions to lay siege to Mainz, Moreaux was ordered to make preparations to capture Luxembourg.

For this mission, Moreaux assembled 19,800 soldiers in the divisions of Jean-Jacques Ambert, Jean-Baptiste Debrun and Guillaume Péduchelle.

[12] Several clashes ensued between the advancing French and the withdrawing Austrians, one in which future marshal of France Louis-Nicolas Davout was involved.

Achille Grigny was his chief of staff and Jean Pierre Alexandre Dieudel commanded the artillery.

Because the roads were in poor condition, it took several weeks before provision convoys began reaching the French camps with regularity.

Moreaux requested reinforcements in order to tighten the blockade and by 15 December the Army before Luxembourg numbered 25,500 men.

On 9 January 1795, the garrison mounted a sortie by 3,000 picked volunteers in order to procure firewood from the surrounding villages.

[1] On 2 February, representative on mission Étienne Neveu appointed Ambert commander of the Army before Luxembourg.

[18] At the end of March, Jacques Maurice Hatry was ordered to undertake the siege with three fresh divisions from the Army of Sambre-et-Meuse.