Javanshir was known for his bravery and intelligence; he fought against the Arabs during the Muslim conquest of Persia on the side of the Sasanian Empire, and was rewarded by the Sasanian king Yazdegerd III himself two golden spears, two golden shields and a flag, probably the Drafsh e Kavian. In 636, he led an Albanian army, which alongside the Armenian prince Mushegh III Mamikonian and Grigor of Syunik, took part in the Battle of al-Qādisiyyah between the Persian and Arab armies. However, the Sasanians were defeated, which made Javanshir lose hope. He then made a mutiny against his overlords and retreated to Caucasian Albania. Where he wrote a letter to Constans II and became an ally of the Byzantine Empire. He was then awarded with the title of "patrikios", and recognized as king of the East. He also married to a noble from a princely family of Syunik.