|Papacy began||18 January 336|
|Papacy ended||7 October 336|
|Died||7 October 336|
|Feast day||7 October|
Little is known of his early life. According to the Liber Pontificalis, he was a Roman, and his father's name was Priscus. Mark succeeded Pope Sylvester I as pope on 18 January 336. He held office only eight months and twenty days, dying on 7 October following.
Some evidence suggests that the early lists of bishops and martyrs known as the Depositio episcoporum and Depositio martyrum were begun during his pontificate. Per the Liber Pontificalis, Pope Mark issued a constitution investing the Bishop of Ostia with a pallium and confirming his power to consecrate newly elected popes. Also per the Liber Pontificalis, Pope Mark is credited with the foundation of the Basilica of San Marco, a basilica in Rome, and a cemetery church over the Catacomb of Balbina, just outside the city on lands obtained as a donation from Emperor Constantine.
Mark died of natural causes and was buried in the catacomb of Balbina. In 1048 his remains were removed to the town of Velletri, and from 1145 were relocated to the Basilica of San Marco in Rome, where they are kept in an urn under the altar. His feast day is celebrated on 7 October. He is particularly venerated at the Abbadia San Salvatore at Monte Amiata.