 He was also a patron of culture and a friend of the philosopher Sallustius.Nothing is known of Marcellinus in his early life; records first mention his name in 454 when he rebelled against Western Emperor Valentinian III following his murder and assassination of Flavius Aëtius who was his friend.He was in Dalmatia at the time and it is believed to have held the title of "Comes rei militaris".