Married to Empress Theodora's niece Sophia, his ties to the imperial family allowed Justin (then kouropalates) to become emperor. He eliminated his rival Justin (son of Germanos) and tried to emulate his predecessor Justinian I unsuccesfully. The unsuccesful foreign policy provoked a war with Persia which resulted in territorial loss; at the same time, Italy was overrun by Lombards. Justin also was a patron of the arts (he sent a silver cross to Rome). Later in his reign, he suffered fits of insanity whereupon Sophia adopted Tiberios II as caesar and successor.

Justin II restored the aqueduct of Valens in 576.