Flavius Petrus Sabbatius, better known as emperor Justinian the Great, was one of the most important early Byzantine rulers. For the past decades, his career has been of particular interest of historians and researchers and this research has produced exceptionally detailed picture of his whole reign. One still insufficiently answered the remaining questions: when the dating of Justinian’s patriciate is possible. Several attempts have been made in modern historiography to approximately determine the year during which Justinian had been granted the prestigious title of patricius, but all of them omit the importance of one key evidence found in the connection with the person and career of magister militum praesentalis Vitalianus. This paper, with regard to all the relevant primary sources and numerous modern studies which are devoted – at least partially – to this topic, proposes a new and more precise dating of the patriciate of Justinian in light of the circumstances surrounding the events of 520 and 521.