[3] In 550, together with his younger brother Justinian, he joined their father in his expedition against Ostrogoth Italy, but Germanus died suddenly in the autumn of 550, before the army had left the Balkans, where it was assembling.

[4][5] After this, Justinian and Germanus's son-in-law, John, led the army towards Salona (modern Split, Croatia), where the eunuch Narses assumed command in late 551.

[7] In early 552, Justin and Justinian were placed at the head of another expedition against a Slavic raid against Illyricum, but their forces were too small to confront the raiders directly.

The Byzantines hastily departed for the town, managing to reach it before the Persian army and then proceeded to successfully defend it during a prolonged siege.

[11] Following this success, in early 556 Justin returned to Nesos to guard it together with Buzes, while the rest of the army marched against the Misimians, a tribe that had recently allied itself with the Persians and killed the Byzantine general Soterichus.

At this time, the Avars demanded to settle in Byzantine imperial territory in Scythia Minor, whose defences had been devastated by a recent Kotrigur invasion led by Zabergan.

With Justin continuing to maintain a careful watch over the Danube river, the Avars contented themselves with the annual subsidy paid by Byzantium, and left the Empire in peace for some years to come.

[16] At the time of Emperor Justinian's death in 565, due to his titles and reputation as a commander, as well his army's proximity to the imperial capital, he was the leading contender for the vacant throne, along with his cousin Justin, the curopalates.

The general was warmly received at first, but soon the new emperor began to make accusations against him, dismissed his bodyguard and placed him under house arrest, before sending him to exile in Alexandria, ostensibly as the new augustal prefect of Egypt.

In reality, he was too great a threat to the new emperor to be left alive; the Visigoth chronicler John of Biclaro explicitly attributes the murder to Justin II's wife, the Empress Sophia.