Possibly of equestrian origin,[1] he began his career probably towards the end of the reign of Marcus Aurelius as a member of the vigintiviri where, as a triumvir capitalis, he managed the prisons in Rome.
In around AD 185, Caesonius Macer continued his climb up the cursus honorum with his appointment as legatus proconsulis, where he assisted the governor of Hispania Baetica in his duties.
This may have been Caesonius Macer's reward for suppressing the revolt of the governor of Hispania Citerior, Lucius Novius Rufus, who was a supporter of Septimius Severus’ rival, Clodius Albinus.
Caesonius Macer's political career under Septimius Severus continued with his first appointment to a consular governorship; he was made legatus augusti pro praetore of Germania Superior, a position he probably held from AD 200 to 203.
Given that Caesonius Macer was around seventy years of age by this time, it has been conjectured that he did not actually accompany the emperor to the east, and that the title was now beginning to be used as an honorific to indicate an individual who was connected to the imperial court.