From his own statements we learn that he travelled in Egypt around 60 BC and that he spent several years in Rome. The latest event mentioned by him belongs to the year 21 BC. He asserts that he devoted thirty years to the composition of his history, and that he undertook frequent and dangerous journeys in prosecution of his historical researches. These assertions, however, find little credit with recent critics. The history, to which Diodorus gave the name Bibliotheca historica ("Historical Library"), consisted of forty books, and was divided into three parts. The first treats of the mythic history of the non-Hellenic, and afterwards of the Hellenic tribes, to the destruction of Troy; the second section ends with Alexander's death; and the third continues the history as far as the beginning of Caesar's Gallic War. Of this extensive work there are still extant only the first five books, treating of the mythic history of the Egyptians, Assyrians, Ethiopians and Greeks; and also the 11th to the 20th books inclusive, beginning with the second Persian War, and ending with the history of the successors of Alexander up to shortly before the Battle of Ipsus (approximately 302 BC). The rest exists only in fragments preserved in Photius and the excerpts of Constantine Porphyrogenitus.
The faults of Diodorus arise partly from the nature of the undertaking, and the awkward form of annals into which he has thrown the historical portion of his narrative. He shows none of the critical faculties of the historian, merely setting down a number of unconnected details. His narrative contains frequent repetitions and contradictions, is without colouring, and monotonous; and his simple diction, which stands intermediate between pure Attic and the colloquial Greek of his time, enables us to detect in the narrative the undigested fragments of the materials which he employed. In spite of its defects, however, the Bibliotheca is of considerable value as to some extent supplying the loss of the works of older authors, from which it is compiled. Unfortunately, Diodorus does not always quote his authorities, but his general sources of information were in history and chronology, Castor, Ephorus and Apollodorus; in geography, Agatharchides and Artemidorus. In special sections he followed special authorities, e.g. in the history of his native Sicily, Philistus and Timaeus.
