[1] A new town was built on its place by the invading Teutonic Knights after they destroyed the original settlement[citation needed] in the late 13th century.

Part of the Order's State, it was given the name Mohrungen after a nearby lake and in 1327 attained Kulm town law from the local commander (Komtur) Hermann von Oettingen.

In 1440, the town joined the anti-Teutonic Prussian Confederation, at the request of which King Casimir IV Jagiellon signed the act of incorporation of the region to the Kingdom of Poland in 1454.

[3] At the start of the subsequent Thirteen Years' War, the citizens sided with Poland, and on June 11, 1454 in Elbing (Elbląg), the town pledged allegiance to the Polish King.

Reconquered by the Elbing commander Heinrich Reuß von Plauen in 1461, the town became his seat as deputy Grand Master.

[2][better source needed] After the peace treaty signed in Toruń in 1466, the town became a part of Poland as a fief held by the Teutonic Knights.

[6]: 2046 During the Polish–Teutonic War of 1519–21, Morąg was again captured by Poland in 1520, after the local commander, Czech mercenary Wurgel Drahnicky, who wanted to defend the castle, was forced to submit to the Poles by the townspeople and his own troops.

[7][better source needed] Upon the Protestant Reformation and the secularisation of the Order's State in 1525 it became part of Ducal Prussia, remaining a Polish fief until 1657.

During the Napoleonic War of the Fourth Coalition, in 1807, Marshal Jean-Baptiste Jules Bernadotte, the future King of Sweden and Norway, took his residence at Dohna Palace; his French forces defeated the advance guard of Levin von Bennigsen's Russian Army at the Battle of Mohrungen on January 25, 1807.

During World War II, some expelled Poles from Mazovia were enslaved by the Germans as forced labour in the town's vicinity.