In any event, Tacitus and others place the Lombards near the mouth of the Elbe; from archeological evidence they appear to have farmed there until the 3rd century CE. They were allies of the king of the Marcomanni and therefore did not participate in the Battle of the Teutoburg Forest, but in 17 CE they and other tribes revolted against him and supported Hermann the Cheruscan, and in 47 CE they restored his nephew to the leadership after the Cheruscans themselves had deposed him. They then participated in an abortive rebellion against Rome alongside the Ubii, but returned peacefully to their homes.

In the 2nd century, many tribes were banding together in confederations: the Franks, Bavarii, Saxons, and above all the Alamanii (whose name means "all people") can be regarded as confederations. One source says the Lombards were subjugated by the Saxons around 300, but rebelled under their king Agelmund.

In the second half of the fourth century, the Lombards started migrating south and east. For a while they were subjugated by "Bulgurs" (probably Huns), but rebelled. In the 540s, King Audoin led them across the Danube into Pannonia, where the Emperor Justinian agreed to subsidize them as fœderati if they would battle the Gepids (an Ostrogothic group).

In 560 a new, energetic king, Alboin, accomplished this task: he subjugated the Gepids and in 566 married Rosamund, the daughter of their king Cunimund. In the spring of 568, Alboin led the Lombards, together with a coalition of Bavarians, Gepids, Saxons, and Bulgars, 400,000 to 500,000 people, across the Alps to invade northern Italy. The first important city to fall was Forum Iulii (Cividale del Friuli), in northeastern Italy, in 569. There, Alboin created the first Lombard duchy, which he entrusted to his nephew Gisulf. Soon Vicenza, Verona and Brescia fell into Germanic hands. In the summer of 569, the Lombards conquered the main Roman centre of northern Italy, Milan. The area was then recovering from the terrible Gothic Wars, and the small Byzantine army left for its defence could do almost nothing for cities away from the coast that could not be supplied by the powerful Byzantine fleet. Pavia fell after a siege of three years, in 572, becoming the first capital city of the new Lombard kingdom of Italy. In the following years, the Lombards penetrated further south, conquering Tuscany and establishing two duchies, Spoleto and Benevento, which soon became semi-independent and even outlasted the northern kingdom, surviving well into the 12th century. The Byzantines managed to retain control of the area of Ravenna and Rome, linked by a thin corridor running through Perugia.

When they entered Italy, some Lombards were still heathen, others Arian Xians. Hence they did not enjoy good relations with the Catholic Church. They gradually adopted Roman names, titles, and religion. They divided their territory into 36 duchies, whose leaders settled in the main cities. The king ruled over them and administered the land through emissaries called gastaldi. But this decentralized form of government was weak, especially given the religious and cultural strife with the locals and increasing conflict between Catholic and Arian leaders within the Lombard hierarchy itself. (From 574 or 575 to 584 or 585, the dukes did not even elect a king.) As the Franks became more and more of a threat, the Lombard kings tried to centralize power over time; but they lost control over Spoleto and Benevento in the attempt. Grimoald (d. 671) managed to regain control over the duchies and deflect an attempt by the Byzantine emperor Constans II to conquer southern Italy; and he also defeated the Franks. Aistulf (d. 756) conquered Ravenna for the Lombards for the first time, but was subsequently defeated by the Frankish king Pippin III, called by the Pope, and had to leave it. The last Lombard king was Desiderius, Duke of Tuscany, who managed to take Ravenna definitively, ending the Byzantine presence in Central Italy, and taking the battle to the Pope, entered Rome in 772, the first Lombard king to do so. But Pope Hadrian I called for help from Charlemagne, who defeated him at Susa and besieged him in Pavia, while his son Adelchis had also to open the gates of Verona to Frankish troops. Desiderius surrendered in 774 and Charlemagne took the title "King of the Lombards" as well and used part of the Lombard territories to create the Papal States.