Marcellinus was a Greek physician who lived and worked during the 4th century CE, in the late period of the Roman Empire. The details of his birthplace and personal life are not recorded. He is known only as the author of a single surviving medical treatise, which shows he was a practicing doctor. His work comes from a time when the complex medical theories of earlier authorities like Hippocrates and Galen were being organized into clearer, practical guides for other physicians.

His known work is a treatise titled On Pulses, which he dedicated to a fellow doctor named Leonides. This text is a systematic handbook on sphygmology, the study of the pulse, which was a core diagnostic method in ancient medicine. It categorizes different types of pulses and connects them to specific diseases and bodily states, serving as a practical tool for diagnosis.

According to modern scholars, Marcellinus's significance lies in his role as a transmitter of classical Greek medical knowledge. His handbook illustrates how complex doctrines, particularly from Galen and earlier pulse theorists like Herophilus, were simplified and adapted for clinical use in the late antique world. The work is therefore a valuable source for understanding the practical application and teaching of medicine during this period of transition.