Marcellus (Greek: Μάρκελλος) was an Eastern Roman judicial official, one of the closest aides of the Byzantine emperor Justinian I (r. 527–565) and commander of the imperial bodyguard of the excubitores in circa 541–552.
[3] In May 541, he was involved in a plot by the Empress Theodora and her close friend Antonina, directed against Emperor Justinian's powerful but widely disliked praetorian prefect, John the Cappadocian.
Theodora resented his influence over Emperor Justinian, while John hated the popular general Belisarius, Antonina's husband.
A meeting was arranged at the palace of Rufinianae near Chalcedon, where Marcellus, along with the eunuch praepositus sacri cubiculi Narses and many soldiers were in attendance to witness the events.
[7] Marcellus was initially reluctant to accuse Artabanes without more proof, and arranged for another discussion between the plotters and Justin to be held, overheard by his concealed associate Leontius.