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.