 On May 20, 1798 Gen. Jan Henryk Dąbrowski nominated him to the post of the commanding officer of the 3rd Battalion of the 1st Legion.He took part in French operations in Italy, but was dismissed on May 18 of the following year, after his soldiers refused to fight against Italian freedom fighters.Dispatched to the newly formed Danube Legion of Gen. Karol Kniaziewicz, Zeydlitz became the commander of the 3rd Battalion of that unit, formally attached to the French 5th Military Division ().