Proba belonged to an influential family of the 4th century, the "Petronii Probi". Her father was Petronius Probianus, Roman consul in 322, while her mother was probably called Demetria. She had a brother, Petronius Probinus, appointed consul in 341; also her grandfather, Pompeius Probus, had been a consul, in 310. Proba married Clodius Celsinus Adelphus, "praefectus urbi" of Rome in 351, thus creating a bond with the powerful "gens" Anicia. They had at least two sons, Quintus Clodius Hermogenianus Olybrius and Faltonius Probus Alypius, who became high imperial officers. She also had a granddaughter Anicia Faltonia Proba, daughter of Olybrius and Tirrania Anicia Juliana.