Some contemporary historians of Procopius claim that Julian II had meant for the general to succeed him instead of Jovian. Whether true or not, Jovian gained the throne and Procopius, an otherwise well-regarded general, dimmed in the background. Jovian soon died, however, and Valentinian became the next emperor. Procopius still had an itch for the position and began to make his moves. Biding his time carefully, he waited for Valentinian's brother and colleague, Valens, to leave on an expedition and with the help of a few key conspirators had himself proclaimed emperor. Because now Valens was away with the bulk of his troops there was nothing that could be immediately done about the insurrection and Procopius was able to hold on to Constantinople and a few adjacent provinces.
By the time Valens had wrapped up with his initial conflict, Procopius had been unable to secure the loyalty of several leading generals and his power base dwindled as Valens approached. Seeing that all was lost he fled but was captured and executed.