Felix, before his ascension to the papacy, is unknown. He is believed to have been Roman. He must have had some position in the Roman Church to be elected after the death of Dionysius. At any rate, he took the throne on January 5, 269.
At this time, the borders of the empire were very porous. Barbarians had been invading periodically for years. Roman soldiers were living throughout Europe and Asia Minor, trying to guard the boundaries. The emperors and generals were routinely going to the ends of the empire to conduct defensive wars. With three different emperors in two years, often due to assassinations and war, the sense of loyalty was disintegrating as fast as the frontiers.
The Roman Church had its own set of problems. Not only was the government disintegrating, not only were there heretics trying to put their spin on Christianity, but now, bishops of the Church were trying to change the early teachings, too.
Soon after Felix was consecrated pope, before news of the death of Dionysius had even reached Asia Minor, he received a report, addressed to the dead pope, of the results of the Synod of Antioch. The bishop of Antioch, Paul of Samosata, had been in trouble with the other bishops for some time, due to his less than orthodox stance on the nature of Jesus. This time they deposed him for his heretical teaching that God the Father existed seperately and completely from Jesus Christ, thus destroying the Trinitarian dogma. Felix responded to the bishops in a long essay on the Trinity, holding up this dogma. Unfortunately, in the 400s, Apollinarius hijacked the work and altered the response to mean almost the opposite and, quoting Felix out of context, tried to argue against the Trinity, again. The argument never stops!
Although Paul was deposed, he refused to give up his episcopacy and his home, which belonged to the Church. Domnus, his appointed successor, could not take his rightful place as the new bishop. Attempts to move Paul out were not successful, so Felix turned to Emperor Aurelian. The emperor was a general and saw himself as a unifier. He sought to subordinate the various religions to the cult of the Unconquered Sun. Unifying one church was in line with his goal. So, when Felix asked for help, Aurelian's reply was that he would recognize whichever bishop was "recognized by the bishops of Italy and of the city of Rome", thus further emphasizing the primacy of Rome.
Back then, a tradition in the Roman Church was to celebrate Mass on the anniversary of a martyr's death over the gravesite. Felix is believed to have given sanction to this custom, although he never began or argued about it.
Felix held the Church together during some hard times, using facts and patience to endure. He probably was not a martyr, being confused with a martyr of the same name. He was buried in the catacombs of Callixtus after his death.
Pope St. Felix, pray for our patience with the world.