On 29 October 1706 he and his army of 5,000 Swedish and 10,000 Polish Soldiers faced an army of 35,000 Russian, Saxon and Polish troops under August the Strong at the Battle of Kalisz and were defeated. His Polish cavalry under Stanisław Leszczyński Grand Duke of Lithuania, was routed. Mardefelt together with 100 officers, including Polish Magnates, was became a prisoner of war. After his release in 1707, Mardefelt died of gout at Ziönloffkoff (Jakin, Poland).