Illus has broken off his relationship with Emperor Zeno, who sends Leontius with an army against Illus, but Illus manages to persuade Leontius to go over to his side.

Zeno remains unpopular with the people of Constantinople, a crucial part of Eastern Roman politics, because he is an Isaurian and as such he is considered a barbarian (which is why he had suffered an usurpation in 475/476 by Basiliscus); Illus, who also is an Isaurian, decides not to take the throne for himself but to raise Leontius to the purple.

Leontius's coronation takes place in Tarsus on July 19, 484—the day had been chosen, following the advice of some astrologers, as a favorable day—at the hands of the empress dowager Verina, who then sends a letter to the Governors of the Diocese of the East and of the Diocese of Egypt suggesting they accept the usurper as Emperor.