[citation needed] He gained the imperial office with his brother Macrianus Minor, after the capture of Emperor Valerian in the Sassanid campaign of 260.

The support of his father, controller of the imperial treasure, and the influence of Balista, Praetorian prefect of the late Emperor Valerian, proved instrumental in his promotion.

[5] Quietus and Macrianus, elected consuls,[6] had to face the Emperor Gallienus, at the time in the West.

Quietus and Balista stayed in the eastern provinces, while his brother and father marched their army to Europe to seize control of the Roman Empire.

After the defeat and deaths of his brother and father in Thrace in 261, Quietus lost the control of the provinces in favour of Septimus Odaenathus of Palmyra, a loyal client king of the Romans who had helped push the Persians out of the eastern provinces and recovered Roman Mesopotamia in 260.