Louis was born while his father Charlemagne was on campaign in Spain, at the Carolingian villa of Cassinogilum, according to Einhard and the anonymous chronicler called Astronomus; the place is usually identified with Chasseneuil, near Poitiers. He was the third son of Charlemagne by his wife Hildegard. His grandfather was Pepin the Short.

Louis was crowned King of Aquitaine as a child in 781 and sent there with regents and a court. Charlemagne constituted the sub-kingdom in order to secure the border of his kingdom after the destructive war against the Aquitanians and Basques under Waifer (capitulated c. 768) and later Hunald II, which culminated in the disastrous Battle of Roncesvalles (778). Charlemagne wanted his son Louis to grow up in the area where he was to reign. However, in 785, wary of the customs his son may have been taking in Aquitaine, Charlemagne sent for him to Aquitaine and Louis presented himself at the Royal Council of Paderborn dressed up in Basque costumes along with other youths in the same garment, which may have made a good impression in Toulouse, since the Basques of Vasconia were a mainstay of the Aquitanian army.

Louis fell ill soon after his final victorious campaigns and went to his summer hunting lodge on an island in the Rhine, by his palace at Ingelheim. On 20 June 840, he died, in the presence of many bishops and clerics and in the arms of his half-brother Drogo, though Charles and Judith were absent in Poitiers. Soon dispute plunged the surviving brothers into a civil war that was only settled in 843 by the Treaty of Verdun, which split the Frankish realm into three parts, to become the kernels of France and Germany, with Burgundy and the Low Countries between them. The dispute over the kingship of Aquitaine was not fully settled until 860. Louis was buried in the Abbey of Saint-Arnould in Metz.[8]