Apart from the author himself, the testimony concerning Marcellinus Comes come from Cassiodorus, who speaks of him in the chapter concerning Roman historians in the Institutiones divinarum humanarumque litterarum (1.17). 

Marcellinus was a native of Illyricum, but repeatedly confirms in his Chronicon that he wrote in the East and that he used the eastern pomp as model; even so, he maintains Latin as his mother tongue, in three passages contrasts Eusebius of Caesarea to noster Jerome (praef; ad 380; ad 382.2), and identifies Plautus as poeta noster (ad 496.2).  He was the cancellarius of Justinian - another native of Illyricum - before the latter became emperor; he was later granted the clarissimatus and the rank of comes (of the second or third order, according to Mommsen), most likely when he quit the office of cancellarius.  We can infer from his office and from many passages of the Chronicon that he lived at Constantinople; Cassiodorus likewise attributes to him four books De temporum qualitatibus et positionibus locorum, which took as their subject the topography minutissima ratione of Constantinople and Jerusalem.  From the testimony of Cassiodorus we know that Marcellinus abandoned secular life and became a monk at an advanced age, before Justinian took the throne.

     Two codices stand as the archetypes of the Chronicon, which covers the period AD 379-534 (excepting an auctarium that is not considered the work of Marcellinus, which continues through AD 548).  The first is codex Sanctomerensis (S); this is held in the city of Saint-Omer, though originally from the Abbey of St. Bertin; it is divided into two parts (n. 697 and n. 706), was assembled in the 10^th c. (or at the start of the 11^th, according to Bethmann), and ends where Marcellinus claims he wished to end in his preface (viz. AD 534).  The second is codex Tilianus Oxoniensis (T), which also preserves the continuation; this was written at the end of the 6^th c. and is therefore nearly coeval with the author; at the end of the 16^th c. it was held by Jean du Tillet (Tilius), the bishop of Meaux, and after various turns subsequently came into the hands of the Bodleian Library (auct. T.II.6), where it was discovered by Mommsen. [S. Rota; tr. C. L. Caterine]