Kléber retired to private life in the peaceful interim after the Treaty of Campo Formio, but returned to military service to accompany Napoleon in the French invasion of Egypt in 1798.

As the invasion started to suffer setbacks, Napoleon returned to Paris in 1799 and appointed Kléber as commander of all French forces in Egypt.

Perhaps the most notable is the Hôtel de Ville at Thann, Haut-Rhin (1787–1793), which was originally designed as a hospital but turned into an administrative building before its completion.

[4] Other surviving buildings are the château of Grandvillars (often erroneously spelled "Granvillars"), built around 1790[5] and the canoness houses of the Benedictine abbey of Masevaux (1781–1790).

[6] The Musée historique de Strasbourg features a room dedicated to Jean-Baptiste Kléber that also displays a number of his sketches and architectural designs.

[2] At the defense of Mainz in July 1793 he so distinguished himself that, though disgraced along with the rest of the garrison and imprisoned, he promptly won reinstatement, and was promoted to brigade general in August 1793.

[2] Kléber was then posted to the Army of the Coasts of La Rochelle and deployed to Western France, where he took part in the suppression of the Revolt in the Vendée.

[7] In these operations began his intimacy with General François Marceau, with whom he defeated the Royalists at the battles of Le Mans and Savenay in December 1793.

[2] When Kléber openly expressed his opinion that the Vendéans merited lenient measures, the authorities recalled him, but reinstated him once more in April 1794 and sent him to the Army of the Ardennes.

[2] In the Syrian campaign of 1799, however, he commanded the vanguard, took El-Arish, Gaza, and Jaffa, and won a great victory at the Battle of Mount Tabor on 15–16 April 1799.

[9] Shortly after these victories, while Kléber was walking in the garden of the palace of Alfi bika, he was stabbed to death by Suleiman al-Halabi, a Kurdish[12] or Arab Syrian student living in Egypt.

The assassin appeared to be begging from Kléber, but then took his hand and stabbed him in the heart, stomach, left arm, and right cheek, before running away to hide near the palace.

His conduct of affairs in Egypt, at a time when the treasury was empty and the troops were discontented for want of pay, shows that his powers as an administrator were little, if at all, inferior to those he possessed as a general.