Born between 720 and 735 in Friuli in Italy to this possibly noble Lombard family, Paul received an exceptionally good education, probably at the court of the Lombard king Ratchis in Pavia, learning from a teacher named Flavian the rudiments of Greek. It is probable that he was secretary to the Lombard king Desiderius, a successor of Ratchis; it is certain that this king's daughter Adelperga was his pupil. After Adelperga had married Arichis II, duke of Benevento, Paul at her request wrote his continuation of Eutropius.
It is certain that he lived at the court of Benevento, possibly taking refuge when Pavia was taken by Charlemagne in 774; but his residence there may be much more probably dated to several years before that event. Soon he entered a monastery on Lake Como, and before 782 he had become a resident at the great Benedictine house of Monte Cassino, where he made the acquaintance of Charlemagne. About 776 his brother Arichis had been carried as a prisoner to Francia, and when five years later the Frankish king visited Rome, Paul successfully wrote to him on behalf of the captive.
His literary attainments attracted the notice of Charlemagne, and Paul became a potent factor in the Carolingian renaissance. In 787 he returned to Italy and to Monte Cassino, where he died on April 13 in one of the years between 796 and 799. His surname Diaconus, shows that he took orders as a deacon; and some think he was a monk before the fall of the Lombard kingdom.
The region of the north, in proportion as it is removed from the heat of the sun and is chilled with snow and frost, is so much the more healthful to the bodies of men and fitted for the propagation of nations, just as, on the other hand, every southern region, the nearer it is to the heat of the sun, the more it abounds in diseases and is less fitted for the bringing up of the human race.Among his sources, Paul used the document called the Origo gentis Langobardorum, the Liber pontificalis, the lost history of Secundus of Trent, and the lost annals of Benevento; he made a free use of Bede, Gregory of Tours and Isidore of Seville.
Cognate with this work is Paul's Historia Romana, a continuation of the Breviarium of Eutropius. This was compiled between 766 and 771, at Benevento. The story runs that Paul advised Adelperga to read Eutropius. She did so, but complained that this Pagan writer said nothing about ecclesiastical affairs and stopped with the accession of the emperor Valens in 364; consequently Paul interwove extracts from the Scriptures, from the ecclesiastical historians and from other sources with Eutropius, and added six books, thus bringing the history down to 553. This work has value for its early historical presentation of the end of the Roman Empire in the West, although it was very popular during the Middle Ages. It has been edited by H Droysen and published in the Monumenta Germaniae Historica. Auctores antiquissimi, Band ii. (1879) as well as by A. Crivellucci, in Fonti per la storia d' Italia, n. 51 (1914).
Paul wrote at the request of Angilram, bishop of Metz (d. 791), a history of the bishops of Metz to 766, the first work of its kind north of the Alps. This Gesta episcoporum Mettensium is published in Band ii. of the Monumenta Germaniae historica Scriptores, and has been translated into German (Leipzig, 1880). He also wrote many letters, verses and epitaphs, including those of Duke/Prince Arichis II of Benevento and of many members of the Carolingian family. Some of the letters are published with the Historia Langobardorum in the Monumenta; the poems and epitaphs edited by Ernst Dümmler will be found in the Poetae latini aevi carolini, Band i. (Berlin, 188f). Fresh material having come to light, a new edition of the poems (Die Gedichte des Paulus Diaconus) has been edited by Karl Neff (Munich, 1908), who denies, however, the attribution to Paul of the most famous poem in the collection, the Ut queant laxis, a hymn to St. John from the initial syllables of the first verses of which Guido d'Arezzo took the names of the first notes of the musical scale. Paul also wrote an epitome, which has survived, of Sextus Pompeius Festus' De significatu verborum. It was dedicated to Charlemagne.
While in Francia, Paul was requested by Charlemagne to compile a collection of homilies. He executed this after his return to Monte Cassino, and it was largely used in the Frankish churches. A life of Pope Gregory the Great has also been attributed to him, and he is credited with a Latin translation of the Greek Life of Saint Mary the Egyptian.