Naum was a disciple and companion of Sts. Cyril and Methodius during the Slavic mission of the 860s–880s. He travelled with them to Rome in 867–869 (where Cyril died and Methodius was consecrated bishop), and he served with Methodius in Moravia until Methodius's death in April 885.
When Pope Stephen V suppressed the Slavonic liturgy in Moravia (885) and the Frankish bishop Wiching expelled the Methodian disciples from Moravia, Naum — together with Clement of Ohrid, Angelar, Sava, and Gorazd (the 'Seven Holy Apostles of the Slavs') — fled south to the Bulgarian kingdom of Boris I, who received them with royal hospitality.
Naum and Clement established the Bulgarian-Slavonic literary culture at the courts of Pliska and later Ohrid: founding the Preslav and Ohrid Literary Schools, producing the Bulgarian-Slavonic translations of the Bible, the Greek liturgical books, the Church Fathers, and secular Greek learning. The Old Church Slavonic literary tradition that the Cyrillo-Methodian-Naumian school produced is the mother-language of Bulgarian, Serbian, Russian, Macedonian, and Ukrainian.
Around 905 Naum withdrew to the south shore of Lake Ohrid, where he founded the monastery of the Holy Archangels (renamed Sveti Naum after his death). He died there on December 23, 910, and was buried at his monastery — which has been a Catholic-Orthodox pilgrim destination for eleven centuries and survives in active liturgical use today.