Initially part of the house guard at the royal residences for Louis XVI, Klein left the military in 1787.

Following the Prussian campaign, he retired from active service, entered politics, and performed administrative duties in Paris.

[4] At the Battle of Ostrach, Klein's cavalry helped to secure the village of Hosskirch, a strategically important forward post, prior to the general engagement.

[5] After the French losses at Ostrach and the subsequent Battle of Stockach, Jourdan ordered a general withdrawal to the Black Forest.

Jourdan placed his chief of staff Jean Augustin Ernouf in provisional command and went to Paris to complain about the state of his army, its equipment and its provisions.

Most of the divisional generals left their posts, except for Pierre Marie Barthélemy Ferino, Joseph Souham, Dominique Vandamme and Klein.

Klein prepared to support either the troops of Jean Thomas Guillaume Lorge or Édouard Adolphe Casimir Joseph Mortier, on the north or south flanks respectively, as required.

In the chaos, Honoré Théodore Maxime Gazan's division, supported by Klein's reserve, pressed the Coalition forces hard at the west end of Constance, by the bridge to the abbey at Petershausen.

[10] Klein's division did not take part in the Battle of Dürenstein, although his dragoons were with Mortier and Gazan immediately prior to the engagement.

[11] Klein's division was part of the decisive defeat of the Austrian and Russian force at the subsequent Battle of Austerlitz three weeks later.

[14] Promotions & Awards In the War of the Fourth Coalition, Klein fought in the Grande Armée under command of Joachim Murat.

[3] After the Battle of Jena-Auerstadt, Klein was with his division of dragoons in the village of Weissensee, the only escape route open to the Prussian General Blücher.

[17] Charles Mullié maintains that Klein vowed revenge; with his division, he pursued and attacked Blücher force the following day.

In 1808, he was raised by letters of patent to a count of the empire and awarded the Grand Cordon of the Order of the Bavarian Lion.

[19] In 1808, Klein divorced Pierron, with the Emperor's permission, and on 2 July of that year remarried to Caroline of Valangin-Arberg, daughter of the Countess of Arberg, a lady-in-waiting to the Empress Josephine de Beauharnais.