After the outbreak of the Warsaw Uprising of 1794, he led his regiment in the city fights and formally replaced the former commander Filip Hauman soon afterwards.
In the battle of Maciejowice, Zeydlitz's regiment fought valiantly against the numerically superior Russian forces and held its positions but at the expense of tremendous losses.
Set free in 1797, he returned to Russia and was then settled in Volhynia, where he founded a secret resistance association, aiming at the removal of Russian forces occupying most of Poland in the aftermath of the partitions.
Gen. Jan Henryk Dąbrowski nominated him to the post of the commanding officer of the 1st Legion's 3rd Battalion.
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.
On 18 December 1830 he was awarded a commemorative medal for 50 years in active service, as the first Polish officer ever.