Of his life nothing is known except that he belonged probably to one of the numerous Irish monasteries of the Frankish Kingdom, became acquainted, by personal observation, with the islands near England and Scotland, and wrote between 814 and 816 an astronomical, and in 825 a geographical work.
More famous is the "De mensura Orbis terrae", a summary of geography, giving concise information about various lands. This work was based upon a "Mensuratio orbis" prepared by order of Theodosius II (435), a manuscript copy of which had found its way to the Carlovingian court. Godescalc had already made use of this copy (781-783) in the composition of his celebrated "Evangelistarium". Dicuil draws also upon Pliny the Elder, Solinus, Orosius, Isidore of Seville, and other authors, and adds the results of his own investigations.
In the nine sections he treats in turn of Europe, Asia, Africa, Egypt, and Ethiopia, the area of the earth's surface, the five great rivers, certain islands, the length and breadth of the Tyrrhenian Sea, and the six (highest) mountains.
Although mainly a compilation, this work is not without value. Dicuil is our only source for detailed information of the surveys carried out under Theodosius II; his quotations, generally exact, are of service for the textual criticism of the authors mentioned; of great interest, too, are the few reports which he got from the travellers of his time; as, for instance, from the monk Fidelis who (762?) journeyed along the canal then still existing, between the Nile and the Red Sea; and from clerics who had visited the Faroe Islands and lived in Iceland for six months.