Olybrius was a son of Sextus Petronius Probus, one of the most influential men of his era and consul in 371, and wife and cousin Anicia Faltonia Proba.
Although they belonged to a traditionally pagan senatorial family, Olybrius and Probinus were Christians.
Arusianus Messius dedicated his Exempla elocutionem to both brothers, and Quintus Aurelius Symmachus addressed a letter to both in 397 (Epistles, v).
He married his cousin Anicia Juliana and had: one son, Anicius Probus (fl.
in 383 and in 392, and great-granddaughter of Lucius Valerius Septimius Bassus and his possible wife Adelphia, as their son's nomina and cognomen suggest; and one daughter, Demetrias.