Pope Marcellinus was the Bishop of Rome or Pope from 30 June 296 to his death in 304. According to the Liberian Catalogue, he was a Roman, the son of a certain Projectus. His predecessor was Pope Caius.
Marcellinus’ pontificate began at a time when Diocletian was Roman Emperor, but had not yet started to persecute the Christians. He left Christianity rather free and so the church’s membership grew. Caesar Galerius led the pagan movement against Christianity and arrived to bring up Diocletian against Christianity in the year 302: first Christian soldiers had to leave the army, later the Church's property was confiscated and Christian books were destroyed. After two fires in Diocletian’s palace he took harder measures against Christians: they had either to apostatize or they were sentenced to death.
Marcellinus is not mentioned in the Martyrologium hieronymianum, or in the Depositio episcoporum, or in the Depositio martyrum. The Liber Pontificalis, basing itself on the Acts of St Marcellinus, the text of which is lost, relates that during Diocletian’s persecution Marcellinus was called upon to sacrifice, and offered incense to idols, but that, repenting shortly afterwards, he confessed the faith of Christ and suffered martyrdom with several companions. Other documents speak of his defection, and it is probably this lapse that explains the silence of the ancient liturgical calendars.