Frederick II was the fifth and last pre-Habsburg Duke of Austria, ruling for more than three decades in the first half of the 13th Century.

He was born on April 25, 1211, in Wiender Neustadt to Duke Leopold VI and Theodora Angelina of Byzantium. He was his parents' second-oldest child, after his brother Henry.

Frederick married twice. His first wife was Eudokia Laskarina, a Byzantine princess. Their marriage ended in 1222. Seven years later, Frederick married Agnes of Merania.

Frederick's older brother, Henry, died in 1228. This made Frederick the heir apparent to the title of Duke of Austria. He assumed that title on July 28, 1230, when his father died. Leopold's last public act had been to end a dispute between the pope and the Holy Roman Emperor. Frederick, by contrast, became known as Frederick the Quarrelsome because he was frequently at war with neighboring lands Bavaria, Bohemia, and Hungary.

Frederick also became at odds with the Holy Roman Emperor, Frederick II. The emperor's son, Henry, had married Duke Frederick's older sister Margaret. When Henry rose up against his father, Duke Frederick sided with Henry. In retaliation, the emperor encouraged King Wenceslaus I of Bohemia to invade Austria. The invaders occupied Vienna, and the emperor had his son Conrad named King of the Romans in that city in 1237. Frederick hunkered down in the imperial residence at Wiener Neustadt and eventually regained the emperor's confidence.

A common enemy appeared in 1241 in the form of the Mongols, who invaded Austria, Croatia, and Hungary. Frederick sent a contingent of soldiers to fight alongside Hungary's King Bêla IV, but internal differences led to the Austrians' early departure, after which the Mongols defeated Hungary. Continuing on, the Mongols encountered a larger Austrian force in Theben; the result was a resounding Austrian victory, convincing the Mongols not to return.

Frederick eliminated one of his enemies in 1246 by marrying his niece Gertrude of Babenberg (daughter of his brother, Henry) to Margrave Vladislaus of Moravia, son of Bohemia's King Wenceslaus.

The Austria-Hungary enmity remained, however, and Frederick and Bêla went to war again, culminating in the Battle of the Leitha River, on June 15, 1246. Frederick died in that battle, ending Babenberg rule in Austria. He had no son; a succession battle ensued.