The town was first mentioned in 1148. At that time it was the seat of a castellan, and a market center, located near the Vistula crossing. In 1205, the Battle of Zawichost was fought nearby, in which Roman the Great of Kingdom of Galicia–Volhynia was defeated by Lesser Poland’s army of Leszek I the White, and Mazovian army of Konrad I of Masovia. It is not known when Zawichost was granted town rights, most probably it happened before 1255. In 1257, prince Bolesław V the Chaste gave the town together with 25 nearby villages to the Order of Poor Ladies. In the 14th century, Zawichost became a royal town and the seat of a starosta. King Kazimierz Wielki built a castle here, which guarded the Vistula crossing.