St Swithun was Bishop of Winchester from his consecration in October 853 until his death on 2 July sometime between 862 and 865. However, he is scarcely mentioned in any document of his own time. His death is entered in the Canterbury manuscript of the Anglo-Saxon Chronicle (MS F) under the year 861. His signature is appended to the witness lists of several Anglo-Saxon charters. Of these charters three belong to 833, 838, 860–862. In the first, Swithun signs as Swithunus presbyter regis Egberti, in the second as Swithunus diaconus, and in the third as Swithunus episcopus.
More than a hundred years later, when Dunstan and Æthelwold of Winchester were inaugurating their church reform, Swithun was adopted as patron of the restored church at Winchester, formerly dedicated to St. Peter and St. Paul. His body was transferred from its almost forgotten grave to Æthelwold's new basilica on 15 July 971, and according to contemporary writers, numerous miracles preceded and followed the move.
The revival of Swithun's fame gave rise to a mass of legendary literature. The so-called Vita S. Swithuni of Lantfred and Wulfstan, written about 1000, hardly contains any biographical fact; all that has in later years passed for authentic detail of Swithun's life is extracted from a biography ascribed to Goscelin of St Bertin's, a monk who came over to England with Hermann, bishop of Salisbury from 1058 to 1078. From this writer we learn that Saint Swithun was born in the reign of Egbert of Wessex, and was ordained priest by Helmstan, bishop of Winchester (838-c. 852). His fame reached the king's ears, and he appointed him tutor of his son, Æthelwulf (alias Adulphus), and considered him one of his chief friends.
Under Æthelwulf, Swithun was appointed bishop of Winchester, to which see he was consecrated by Archbishop Ceolnoth. In his new office he was known for his piety and his zeal in building new churches or restoring old ones. At his request Æthelwulf gave the tenth of his royal lands to the Church. Swithun made his diocesan journeys on foot; when he gave a banquet he invited the poor and not the rich. William of Malmesbury adds that, if Bishop Ealhstan of Sherborne was Æthelwulf's minister for temporal matters, Swithun was the minister for spiritual matters.
Swithun's best known miracle was his restoration on a bridge of a basket of eggs that workmen had maliciously broken. Of stories connected with Swithun the two most famous are those of the Winchester egg-woman and Queen Emma's ordeal. The former is to be found in Goscelin's Life (c. 1100), the latter in Thomas Rudborne's Historia major (15th century), a work which is also responsible for the not improbable legend that Swithun accompanied Alfred on his visit to Rome in 856. He died on 2 July 862. On his deathbed Swithin begged that he should be buried outside the north wall of his cathedral where passers-by should pass over his grave and raindrops from the eaves drop upon it.