He was the son of Clodius Celsinus Adelphius, who had been praefectus urbi in 351, and of Faltonia Betitia Proba, a poet.
[2][3][4] He reached the rank of vir clarissimus, then consularis of Campania (before 361 he is attested as patron of Formia), proconsul of Africa Province (361), praefectus urbi of Rome (369-370), Praetorian prefect of Illyricum, Praetorian prefect of the East, and consul in 379.
During his office as praefectus urbi, which was generally calm and balanced, he arrested two suspected poisoners.
Olybrius had been appointed prefect of Illyricum by emperor Gratian probably at the beginning of 378, in the wake of the preparations for the war against the Goths in Thracia that led to the defeat and death of emperor Valens in the Battle of Adrianople in August of that year.
Symmachus tells that he discovered that Olybrius was behind this misappropriation and that some of the agents had tried to avoid the restitution of the stolen property, even kidnapping people and bribing witnesses.