The castle was built between 1346–1353 and by then it had one wing on the north-east side of the rectangular courtyard.
Access to the castle lead from the drawbridge over the river Łyna, surrounded by a belt of defensive walls and a moat.
The south-west wing of the castle was built in the 15th century, the tower situated in the west corner of the courtyard, from the middle of the 14th century, was rebuilt in the early 16th century and had a round shape on a square base and was 40 meters high.
At the same time the castle walls were raised to a height of 12 meters and a second belt of the lower walls was built.
The castle walls were partly combined with city walls, which made the castle look like it had been a powerful bastion defending access to the city.

The castle was owned by Warmia Chapter, which until 1454, together with the Prince-Bishopric of Warmia, was under military protection of the Teutonic Knights and their Monastic State of Prussia.

The castle had played a huge role in the Polish-Teutonic wars by then.
After the Battle of Grunwald in 1410, the Poles took it after a few days siege.
In the Thirteen Years' War (1454–66) it was jumping from rule to rule.
The Knights threatened the castle and the town in 1521, but the defence was very effective.
They contained one failed assault.
There is a connection between the history of the castle, the city of Olsztyn, and Nicolaus Copernicus.
He prepared the defence of Olsztyn against the invasion of the Teutonic Knights.

In the sixteenth century, there were two prince-bishops of Warmia that stayed there: Johannes Dantiscus – the first sarmatian poet, endowed with the imperial laurel wreath for "Latin Songs" (1538, 1541) and Marcin Kromer, who wrote with equal ease in Latin and Polish scientific and literary works (1580).
Kromer consecrated the chapel of St. Anna, which was built in the south-west wing of the castle.
In the course of time both wings of the castle lost military importance, which for residential purposes has become very convenient.
In 1779 Prince-Bishop Ignacy Krasicki stopped here as well.

After the Prussian annexation of Warmia during the First Partition of Poland in 1772, the castle became the property of the state board of estates (War and Domain Chamber, Kriegs- und Domänenkammer).
In 1845 the bridge over the moat was replaced by a dam better connecting the castle with the city.
In 1901–1911 a general renovation of the castle was performed, however several sections of the building were violated at the same time where they changed the original look of the castle e.g. putting on window frames in a cloister.
The tower was crowned in 1921 and again in 1926 in the halls of the castle, became a museum.

In 1945 the whole castle became home to the Masurian Museum, which today is called the Museum of Warmia and Masuria.
In addition there are also popular events held within the frameworks of the Olsztyn Artistic Summer and so called "evenings of the castle" and "Sundays in the Museum".
The castle was built between 1346–1353 and by then it had one wing on the north-east side of the rectangular courtyard. Access to the castle lead from the drawbridge over the river Łyna, surrounded by a belt of defensive walls and a moat. The south-west wing of the castle was built in the 15th century, the tower situated in the west corner of the courtyard, from the middle of the 14th century, was rebuilt in the early 16th century and had a round shape on a square base and was 40 meters high. At the same time the castle walls were raised to a height of 12 meters and a second belt of the lower walls was built. The castle walls were partly combined with city walls, which made the castle look like it had been a powerful bastion defending access to the city. 
The castle was owned by Warmia Chapter, which until 1454, together with the Prince-Bishopric of Warmia, was under military protection of the Teutonic Knights and their Monastic State of Prussia.
The castle had played a huge role in the Polish-Teutonic wars by then. After the Battle of Grunwald in 1410, the Poles took it after a few days siege. In the Thirteen Years' War (1454–66) it was jumping from rule to rule. The Knights threatened the castle and the town in 1521, but the defence was very effective. They contained one failed assault. There is a connection between the history of the castle, the city of Olsztyn, and Nicolaus Copernicus. He prepared the defence of Olsztyn against the invasion of the Teutonic Knights.
In the sixteenth century, there were two prince-bishops of Warmia that stayed there: Johannes Dantiscus – the first sarmatian poet, endowed with the imperial laurel wreath for "Latin Songs" (1538, 1541) and Marcin Kromer, who wrote with equal ease in Latin and Polish scientific and literary works (1580). Kromer consecrated the chapel of St. Anna, which was built in the south-west wing of the castle. In the course of time both wings of the castle lost military importance, which for residential purposes has become very convenient. In 1779 Prince-Bishop Ignacy Krasicki stopped here as well.
After the Prussian annexation of Warmia during the First Partition of Poland in 1772, the castle became the property of the state board of estates (War and Domain Chamber, Kriegs- und Domänenkammer). In 1845 the bridge over the moat was replaced by a dam better connecting the castle with the city. In 1901–1911 a general renovation of the castle was performed, however several sections of the building were violated at the same time where they changed the original look of the castle e.g. putting on window frames in a cloister. The tower was crowned in 1921 and again in 1926 in the halls of the castle, became a museum.
In 1945 the whole castle became home to the Masurian Museum, which today is called the Museum of Warmia and Masuria. In addition there are also popular events held within the frameworks of the Olsztyn Artistic Summer and so called "evenings of the castle" and "Sundays in the Museum".
Olsztyn