The town was first mentioned in 1065 as a castle in the border of the Polatsk Principality with the Lithuanian tribes. Archaeologists excavated a Viking settlement in the village of Maskachichy not far from the town. They think that Viking mercenaries were used as dependable border guards. In the 14th century, Braslaw was incorporated into the Grand Duchy of Lithuania and, in fact, became an important fortification near the disturbing line with the Livonian Order in the 14 – 15th centuries. In 1500, Alexander Jagiellon privileged the townsfolk with a limited self-administration right and the coat of arms. In 1506, the castle was presented to the widowed queen Yelena Ivanovna, the daughter of Ivan III of Russia and wife of Alexander Jagiellon, who founded here an Orthodox Christian nunnery. The town was much developed thanks to its praepostor Lev Sapeha and the king Stanisław August Poniatowski.
In 1795 - 1919, Braslaw was occupied by Russia. It became an uyezd center (county seat) in Vilna Governorate in 1795, later in Kovno Governorate in 1843 except brief French occupation in 1812. It was occupied by German Empire for 10 months in 1918. According to the Treaty of Riga, it became Polish. It was poviat center (county seat) in Wilno Voivodeship. In 1939, it was appended to the Belarusian Soviet Socialist Republic. It was occupied by Nazi Germany between 27 June 1941 and 6 June 1944. A witness to the Jews of Braslaw being forced to walk to the site of their execution stated, "The column of Jews was supervised by Latvians and Lithuanians. A women wanted to save her child by pushing him aside, but a policemen saw and put the child back into the column once again." It was a raion center firstly in Vileyka Voblast, later in Polatsk Voblast between 1944 and 1954 and finally in Molodechno Voblast between 1954 and 1960 before passing to Vitebsk one.
Since the 1920s, Braslaw was developed as a cheap summer resort. In 1995, it accommodated the main office of the National Park of the Braslaw Lakes.