The castellan’s town was first mentioned in 1233. In 1501 Brok was granted its town charter. In the 16th century it was one of the greatest towns of Masovia. The town was owned and seated by the Bishops of Płock.
Since 1795 it was under Prussian rule. Since 1807 it transferred to the Duchy of Warsaw, and since 1815 it belonged to the Kingdom of Poland (Congress Poland). In 1869, the tsar authorities deprived Brok of its town rights.
In 1922, Brok regained its town charter.
During World War II, in September 1939, there was a lot of fighting between Polish and German Armies in Brok. The town was burnt down at that time. In 1944, Brok was liberated by the Soviet Army.