Leopold III was the sixth Margrave of Austria. He ruled for more than four decades in the late 11th Century and early 12th Century.

Leopold was born in 1073, at Babenberg Castle in Gars am Kamp. His father was the fifth Magrave of Austria, Leopold II, and his mother was Ida of Formbach-Ratelnberg.

The younger Leopold was 23 when his father died, in 1095. The new margrave, Leopold III, set about solidifying his hold on power. His father had challenged the powerful Holy Roman Emperor, Henry IV, and had seen his power and influence greatly diminished as a result. By the close of the 11th Century, however, the emperor was preoccupied with stamping out a number of rebellions.

One of those rebels was the emperor's son, also named Henry. Leopold III threw in his lot with Henry the son and, in 1106, married Agnes, daughter of Henry IV and brother of the eventual Henry V. (Leopold had been married once before; sources do not agree on the name of that first wife, who died in 1105. From that marriage came a son, Adalbert.) Leopold and Agnes had ten children: Leopold, Henry, Berta, Agnes, Ernst, Otto, Conrad, Elizabeth, Judith, and Gertrude.

Leopold III is known for establishing a number of monasteries, among them the famous Klosterneuburg Monastery, just north of what is now Vienna. He encouraged the growth of settlements surrounding these monasteries and also the growth of cities in general.

Leopold's reign was a long one. He outlived both Holy Roman Emperors Henry IV and Henry V and was largely free to manage his own affairs during the latter stages of the Investiture Controversy, which the Concordat of Worms settled in 1122. Leopold died in 1136 and was succeeded his son, who became Leopold IV.