Career
When Rumelian beglerbey and vizier Hadım Şehabeddin was defeated by John Hunyadi in 1442, he was replaced by Kasim Pasha at both positions. At the beginning of the John Hunyadi crossed the Danube and rushed south along the river Morava to attack forces of Kasim Pasha before he could mobilize his complete army. The cavalry forces of 12,000 commanded by Kasim Pasha were defeated near Aleksinac during the Battle of Niš in 1443.
After an Ottoman defeat, the retreating forces of Kasim Pasha and Turakhan Bey burned all villages between Niš and Sofia.
Turakhan Bey and Kasim Pasha met each other again in Sofia from where Kasim sent the messenger to Edirne to alert Sultan. Kasim Pasha commanded Ottoman forces that chased Christian army after the Battle of Zlatica held at the end of 1443.
His army was defeated on 24 December 1444 on Melštica near Sofija and many Ottoman officers were captured by Christian army. When the Sultan banished Turahan Bey to a prison, Kasim allegedly complained to Çandarlı Halil Pasha that Turahan"s subordinated officers should be banished too.
When his complaint was refused, Kasim resigned from the position of Rumelia beylerbey.