In the first half of 1649, the Polish–Lithuanian Commonwealth negotiations with the rebellious Cossacks fell through, and the Polish-Lithuanian military begun gathering near the borders with the insurgent-held Ukraine.

[5] Zbarazh Castle was rebuilt in the decades preceding the siege under the Netherland engineer Henryk van Peene, who finished his project in 1626.

[6] It was a relatively modern and resilient construction, whose major weakness was its small size, and correspondingly, little space for any extensive army and required supplies.

[5] However, as noted by Polish historian Widacki, Firlej had little authority, and often listened to Wiśniowiecki's advice, who could be seen as the real commander of the Polish-Lithuanian forces.

[11] The first skirmish near the main camp, however, resulted in the Polish-Lithuanian victory, as the Cossack and Tatar forces were thrown back, which raised the defenders morale.

[12] After the failure of those early assaults, the Cossack and Tatar army began a regular siege, constructing their own field fortifications, and intensifying the artillery bombardment of the Polish-Lithuanian camp.

[15] In the meantime, the Cossack and Tatars would try to extend their fortifications closer to the defender's line; they launched their last large assault on 6 August, but were defeated once more.

[16] In the meantime, at Zbarazh, the besiegers even managed to successfully dig a tunnel into the Polish-Lithuanian camp around 16 August, but it was destroyed by the defenders.