The remnants of a fortified settlement in what is now the Stare Bielsko (Old Bielsko) district of the city were discovered between 1933 and 1938 by a Polish archaeological team.
The settlement was dated to the 12th - 14th centuries.
Its dwellers manufactured iron from ore and specialized in smithery.
The current centre of the town was probably developed as early as the first half of the 13th century.
At that time a castle (which still survives today) was built on a hill.

In the second half of the 13th century, the Piast dukes of Opole invited German settlers to colonize the Silesian Foothills.
As the dukes then also ruled over the Lesser Polish lands east of the Biała River, settlements arose on both banks like Bielitz (now Stare Bielsko), Nickelsdorf (Mikuszowice Śląskie), Kamitz (Kamienica), Batzdorf (Komorowice Śląskie) and Kurzwald in the west as well as Kunzendorf (Lipnik), Alzen (Hałcnów) and Wilmesau (Wilamowice) in the east.
Nearby settlements in the mountains were Lobnitz (Wapienica) and Bistrai (Bystra).

After the partition of the Duchy of Oppeln in 1281, Bielsko passed to the Dukes of Cieszyn (Teschen).
The town was first documented in 1312 when Duke Mieszko I of Cieszyn granted a town charter.
The Biała again became a border river, when in 1315 the eastern Duchy of Oświęcim split off from Cieszyn as a separate under Mieszko's son Władysław.
After the Dukes of Cieszyn had become vassals of the Bohemian kings in 1327 and the Duchy of Oświęcim was sold to the Polish Crown in 1457, the Biała River for centuries marked the border between the Bohemian crown land of Silesia within the Holy Roman Empire and the Lesser Polish region of the Kingdom of Poland and the Polish–Lithuanian Commonwealth.

With Bohemia and the Upper Silesian Duchy of Cieszyn, Bielsko in 1526 was inherited by the Austrian House of Habsburg and incorporated into the Habsburg Monarchy.
From 1560 Bielsko was held by Frederick Casimir of Cieszyn, son of Duke Wenceslaus III Adam, who due to the enormous debts his son left upon his death in 1571, had to sell it to the Promnitz noble family at Pless.
With the consent of Emperor Maximilian II, the Promnitz dynasty and their Schaffgotsch successors ruled the Duchy of Bielsko as a Bohemian state country; acquired by the Austrian chancellor Count Friedrich Wilhelm von Haugwitz in 1752, the ducal status was finally confirmed by Empress Maria Theresa in 1754.

After the Prussian king Frederick the Great had invaded Silesia, Bielsko remained with the Habsburg Monarchy as part of Austrian Silesia according to the 1742 Treaty of Breslau.

In late 1849 Bielsko became a seat of political district.
In 1870 it became a statutory city.
The remnants of a fortified settlement in what is now the Stare Bielsko (Old Bielsko) district of the city were discovered between 1933 and 1938 by a Polish archaeological team. The settlement was dated to the 12th - 14th centuries. Its dwellers manufactured iron from ore and specialized in smithery. The current centre of the town was probably developed as early as the first half of the 13th century. At that time a castle (which still survives today) was built on a hill.
In the second half of the 13th century, the Piast dukes of Opole invited German settlers to colonize the Silesian Foothills. As the dukes then also ruled over the Lesser Polish lands east of the Biała River, settlements arose on both banks like Bielitz (now Stare Bielsko), Nickelsdorf (Mikuszowice Śląskie), Kamitz (Kamienica), Batzdorf (Komorowice Śląskie) and Kurzwald in the west as well as Kunzendorf (Lipnik), Alzen (Hałcnów) and Wilmesau (Wilamowice) in the east. Nearby settlements in the mountains were Lobnitz (Wapienica) and Bistrai (Bystra).
After the partition of the Duchy of Oppeln in 1281, Bielsko passed to the Dukes of Cieszyn (Teschen). The town was first documented in 1312 when Duke Mieszko I of Cieszyn granted a town charter. The Biała again became a border river, when in 1315 the eastern Duchy of Oświęcim split off from Cieszyn as a separate under Mieszko's son Władysław. After the Dukes of Cieszyn had become vassals of the Bohemian kings in 1327 and the Duchy of Oświęcim was sold to the Polish Crown in 1457, the Biała River for centuries marked the border between the Bohemian crown land of Silesia within the Holy Roman Empire and the Lesser Polish region of the Kingdom of Poland and the Polish–Lithuanian Commonwealth.
With Bohemia and the Upper Silesian Duchy of Cieszyn, Bielsko in 1526 was inherited by the Austrian House of Habsburg and incorporated into the Habsburg Monarchy. From 1560 Bielsko was held by Frederick Casimir of Cieszyn, son of Duke Wenceslaus III Adam, who due to the enormous debts his son left upon his death in 1571, had to sell it to the Promnitz noble family at Pless. With the consent of Emperor Maximilian II, the Promnitz dynasty and their Schaffgotsch successors ruled the Duchy of Bielsko as a Bohemian state country; acquired by the Austrian chancellor Count Friedrich Wilhelm von Haugwitz in 1752, the ducal status was finally confirmed by Empress Maria Theresa in 1754.
After the Prussian king Frederick the Great had invaded Silesia, Bielsko remained with the Habsburg Monarchy as part of Austrian Silesia according to the 1742 Treaty of Breslau.
In late 1849 Bielsko became a seat of political district. In 1870 it became a statutory city.
Bielsko-Biała