The area around Mosonmagyaróvár has been inhabited since the 5th millennium BC, but settlement of the city proper can only be traced to around the 1st century, which was when the Roman Empire was extended to the Danube, creating the province of Pannonia. The Romans established a camp called Ad Flexum (Latin: “towards the bend”) at the site of Mosonmagyaróvár; it is likely that the Hungarians from the Árpád era would name the place Óvár due to the Roman ruins which would still be present during the 11th century.
After the Honfoglalás, King Stephen ordered the building of a castle at Moson to defend the border. Settlers flocked around the wooden and then stone castle, and by the 11th century it was described as a strong fortress and bustling merchant town; by this time, it was also the county seat of Moson. However, in 1030, the Holy Roman Emperor Conrad II was able to conquer the castle on his way to the Rába. During the Crusades, Kálmán, King of Győr and Moson, was able to defeat a Swabian–Bavarian army of 15,000 men from the castle. There was significant industrial and urban development during the 13th century, when Moson once again found itself along a trade route. Mills and churches were built during this time. All advances were destroyed, however, by Ottokar II, a Czech king, when he leveled the castle at Moson in 1271.
Béla IV, King of Hungary at the time, did not consider it worthwhile to try and rebuild the castle at Moson, and thus turned to Óvár as a promising site for a future fortress. The King gave a man named Conrad, who was of the Győr tribe, lands in Moson and funds to be able to accomplish this task. Though he made significant improvements to the castle, he defected to Ottokar II and Duke Albert of Austria. For this impunity, he was deprived of his lands, and from then on Óvár was an estate of the Hungarian queens. The first settlers to Óvár were refugees from the destroyed Moson, and in the 14th century it became a bustling city with new industry and urbanization. Mills along the Lajta became a source of employment and attention, as many were owned by the royal house. In 1354, Queen Elisabeth gave Óvár the title of “queen’s town”. This gave the townspeople the right to elect their own parish priest, have their own jurisdiction, inherit possessions, and pay no customs in all of Hungary. Later kings recognized these rights, but the townspeople still had to struggle to maintain them. After Louis II‘s marriage to Mary of Habsburg, Óvár became a key defense on the Austrian border, which would come into play during the Turkish invasion.
In 1683, the new castle was helpless against the retreating Turkish army, which had been repulsed again at Vienna. Both Moson and Magyaróvár were set ablaze. Though the town archives were now completely destroyed, the damage was repaired more quickly this time around, at least quickly enough to allow Rákóczi to use the castle as a base during his war for independence from the Habsburgs. In 1721, after the revolution was crushed, the castle at Magyaróvár lost its strategic importance, and all military materiel was transferred to Bratislava. However, the town prospered greatly after the war, with the establishment of new guilds, a town doctor, and the Piarist school. The Austrian government wished to limit the independence of the town, but the people were able to hold on to a degree of autonomy; an agreement to this effect was signed in 1796 after delegates had been sent to Vienna and Buda. In 1809, Napoleon‘s army demanded the town’s provisions for his wars of conquest, and although this impoverished the people, they saved the town from destruction.
During the First World War, the Austrians maintained an armory in Magyaróvár. As a consequence of the Treaty of Trianon, most of Moson county was lost to non-Hungarian lands and all signs of the Habsburg rule were destroyed. What followed was another period of peace, during which time Moson and Magyaróvár were administratively unified as Mosonmagyaróvár. However, cultural differences, and even rivalry, were to persist well into the later twentieth century. During the Second World War, unemployment plummeted and the town’s industry prospered. The town did not suffer much damage during the war; in 1946, its significant German population was deported. In 1948 bus services were created. During the later 1940s most of the town’s institutions were nationalized by the communist regime. As many as 50 protesting civilians were killed during the revolution of ’56, and the town was slow to recover. During the communist years, a new “town center” was developed between the existing Medieval centers of Moson and Magyaróvár, and there was significant development, including the opening of a university, new schools, and other public projects.
After the reestablishment of the current Representative Parliamentary Democracy in 1989, the Young Democrats controlled the city administration for a few years, expanding tourism and making developments to the gas and sewage infrastructure. Notably, the Piarist school was reopened.