Cassius Dio was named praetor by Emperor Pertinax (r. 193) and Barnes thinks he served in this office in 195. He was Roman consul twice, perhaps in A.D. 205/6 or 222, and then again in 229. Dio was a friend of the emperors Septimius Severus and Macrinus. Dio served his second consulship with Emperor Severus Alexander. After his second consulship, Dio retired from political office and went home to Bithynia,
Cassius Dio wrote a history of the Civil Wars of 193-7 and a history of Rome from its foundation to the death of Severus Alexander (in 80 books). Dio's history was written in Greek. Only a few of the books of this history of Rome have survived. Much of what we know of the writing of Cassius Dio comes from Byzantine scholars. The Suda credits him with a Getica (actually written by Dio Chrysostom) and a Persica (actually written by Dinon of Colophon, according to Alain M. Gowing, in "Dio's Name," (Classical Philology, Vol. 85, No. 1. (Jan., 1990), pp. 49-54).