Born in Rome, he succeeded Pope Dionysius and is noted for his theological contributions, particularly a significant dogmatic letter addressing the unity of Christ’s person.

The intervention of Emperor Aurelian, prompted by Felix, led to Paul’s deposition from the bishopric of Antioch, reinforcing orthodox Christological doctrine.

[2][3] Felix is traditionally credited with instituting the practice of celebrating Mass over the tombs of martyrs, though this attribution remains a subject of historical debate.

[9] The notice about Felix in the Liber Pontificalis ascribes to him a decree that Masses should be celebrated on the tombs of martyrs ("Hic constituit supra memorias martyrum missas celebrare").

[10] The latter detail is evidently an error, for the fourth-century Roman calendar of feasts says that Pope Felix was interred in the Catacomb of Callixtus on the Via Appia.

Thereafter, the feast of Saint Felix I, no longer mentioned in the General Roman Calendar, is celebrated on his true day of death, 30 December, and without the qualification of "martyr".

[12] According to more recent studies, the oldest liturgical books indicate that the saint honoured on 30 May was a little-known martyr buried on the Via Aurelia, who was mistakenly identified with Pope Felix I,[13] an error similar to the identification in the liturgical books of the martyr saint celebrated on 30 July with the antipope Felix II, corrected in the mid-1950s.