| Marcus I of Byzantium | |
| Patriarch Of: | Bishop of Byzantium |
| Enthroned: | 198 |
| Ended: | 211 |
| Predecessor: | Olympianus of Byzantium |
| Successor: | Philadelphus of Byzantium |
| Religion: | Early Christianity |
Marcus I (el|Μᾶρκος; died 211) was the bishop of Byzantium for 13 years (198 - 211 AD). He succeeded Bishop Olympianus. His term of office took place during the persecution of Christians by Emperor Septimius Severus. His successor was Philadelphus.