Paschasius was an orphan adopted by the convent of Notre-Dame at Soissons. He entered Corbie Abbey in Picardy as a young man and was educated there under Abbots Adalhard and Wala. He served as schoolmaster of Corbie for many years and was briefly abbot (843–851) before resigning to return to scholarly work.
His De Corpore et Sanguine Domini (c. 831) — the first treatise systematically devoted to the Eucharist in the history of theology — argued explicitly that the bread and wine of the Eucharist become substantially the historical Body and Blood of Christ born of the Virgin. This realist doctrine, controversial in its own day (Ratramnus of Corbie wrote a treatise of the same name defending a more symbolic interpretation), prevailed at the Synod of Vercelli (1050) and was definitively confirmed by the Fourth Lateran Council (1215) as the doctrine of transubstantiation. Paschasius is the originator of the dogmatic vocabulary of Eucharistic Real Presence in Latin theology.
He died at Corbie in 865 after spending the last fifteen years of his life as an ordinary monk.