His early years were partly spent at the court of his grandfather, Charlemagne, whose special affection he is said to have won. When the emperor Louis divided his dominions between his sons in 817, Louis received Bavaria and the neighbouring lands, but did not undertake the government until 825, when he became involved in war with the Wends and Sorbs on his eastern frontier. In 827 he married Emma, sister of his stepmother Judith, and daughter of Welf I, whose possessions ranged from Alsace to Bavaria. Louis soon began to interfere in the quarrels arising from Judith's efforts to secure a kingdom for her own son Charles (later known as Charles the Bald), and the consequent struggles of Louis and his brothers with the emperor Louis I.
When the elder Louis died in 840 and his eldest son Lothar claimed the whole Empire, Louis allied with his half-brother, (now) king Charles the Bald, and defeated Lothar at Fontenoy in June 841. In June 842, the three brothers met on an island in the Saone to negotiate a peace, and each appointed forty representatives to arrange the boundaries of their respective kingdoms. This developed into the Treaty of Verdun concluded in August 843, by which Louis received the bulk of the lands of the Carolingian empire lying east of the Rhine, together with a district around Speyer, Worms and Mainz, on the left bank of the river. His territories included Bavaria, where he made Regensburg the centre of his government, Thuringia, Franconia and Saxony. He may truly be called the founder of the German kingdom, though his attempts to maintain the unity of the Empire proved futile. Having in 842 crushed a rising in Saxony, he compelled the Obotrites to own his authority, and undertook campaigns against the Bohemians, the Moravians and other tribes, but was not very successful in freeing his shores from the ravages of Danish pirates.
At his instance, synods and assemblies were held where laws were decreed for the better government of church and state. In 853 and the following years, Louis made more than one attempt to secure the throne of Aquitaine, which, according to the Annals of the Abbey of Fulda (Annales Fuldensis), the people of that country offered him in their disgust with the cruel misrule of Charles the Bald. Louis met with sufficient success to encourage him to issue a charter in 858, dated "the first year of the reign in West Francia," but treachery and desertion in his army, and the loyalty to Charles of the Aquitanian bishops brought about the failure of the enterprise, which Louis renounced by a treaty signed at Coblenz on June 7, 860.
In 855 the emperor Lothar died, and Louis and Charles for a time seem to have cooperated in plans to divide Lothar's possessions among themselves -- the only impediments to this being Lothar's sons, Lothar II and Louis II. In 868 at Metz they agreed definitely to a partition; but when Lothar II died in 869, Louis the German was lying seriously ill, and his armies were engaged with the Moravians. Charles the Bald accordingly seized the whole kingdom; but Louis the German, having recovered, compelled him by a threat of war to agree to the treaty of Mersen, which divided it between the claimants.
The later years of Louis the German were troubled by risings on the part of his sons, the eldest of whom, Carloman, revolted in 861 and again two years later; an example that was followed by the second son Louis, who in a further rising was joined by his brother Charles. A report that the emperor Louis II was dead led to peace between father and sons and attempts by Louis the German to gain the imperial crown for Carloman. These efforts were thwarted by Louis II, who was not in fact dead, and his uncle, Charles the Bald.
Louis was preparing for war when he died on September 28, 876 at Frankfurt. He was buried at the abbey of Lorsch, leaving three sons and three daughters. Louis was in war and peace alike the most competent of the descendants of Charlemagne. He obtained for his kingdom a certain degree of security in face of the attacks of Normans, Hungarians, Moravians and others. He lived in close alliance with the Church, to which he was very generous, and entered eagerly into schemes for the conversion of his heathen neighbours