According to his hagiography by Theophylact of Ohrid, Clement knew the life of Methodius like no other. That is why most scholars think he was born in Byzantine empire in the territory where Methodius served during his political career, i.e. that he was a Slav from Southern Macedonia. According to others, the area of Southern Macedonia, where he was born, was then part of Bulgaria. Most of Macedonia became part of Bulgaria in 830s and in 840s, i.e when Clement was born. The Short Life of St. Clement by Theophylact of Ohrid testimonies his Slavic origin, calling him the first bishop, who used to preach in Bulgarian language, while "The Ohrid Legend" written by Demetrios Chomatenos calls him a Bulgarian, who was born somewhere in Macedonia. Because of that, some scholars label him as Bulgarian Slav, while Dimitri Obolensky calls Clement a Slav inhabitant of the Kingdom of Bulgaria.
A fringe view on his origin is saying Clement was born in Great Moravia. This view is based on the lexicographical analysis of Clement's works.
The exact date of his birth is unknown. Most probably he joined Methodius as a young man following him later to the monastery on Mysian Olympus.
Clement participated in the mission of Cyril and Methodius to Great Moravia. After the death of Cyril, Clement accompanied Methodius on his journey from Rome to Pannonia and Great Moravia. After the death of Methodius himself in 885, Clement headed the struggle against the German clergy in Great Moravia along with Gorazd. After spending some time in jail, he was expelled from Great Moravia and in 885 or 886 reached Belgrade, then in the borders of Bulgaria together with Naum of Preslav, Angelarius and possibly Gorazd (according to other sources, Gorazd was already dead by that time). Thereafter, the four of them were sent to the Bulgarian capital of Pliska where they were commissioned by Boris I of Bulgaria to instruct the future clergy of the state in the Slavonic language.
After the adoption of Christianity in 865, religious ceremonies in Bulgaria were conducted in Greek by clergy sent from the Byzantine Empire. Fearing growing Byzantine influence and weakening of the state, Boris viewed the adoption of the Old Slavonic language as a way to preserve the political independence and stability of Bulgaria. With a view thereto, Boris made arrangements for the establishment of two literary academies where theology was to be taught in the Slavonic language. The first of the schools was to be founded in the capital, Pliska, and the second in the region of Kutmichevitsa.
According to his hagiography by Theophylact of Ohrid, while Naum stayed in Pliska working on the foundation of the Pliska Literary School, Clement was commissioned by Boris I to organise the teaching of theology to future clergymen in Old Church Slavonic in the southwestern part of the Bulgarian Empire, in the region then known as Kutmichevitsa. For a period of seven years (between 886 and 893) Clement taught some 3,500 disciples in the Slavonic language and the Glagolitic alphabet. At that time Clement translated a rich Christian literature in Old Church Slavonic, and in this way, he and his co-workers, laid the foundations of the Bulgarian Orthodox Church. In 893 he was ordained archbishop of Drembica, Velika (bishopric). Upon his death in 916 he was buried in his monastery, Saint Panteleimon, in Ohrid. Soon after he was canonized as a saint by the Bulgarian Orthodox Church.
The development of Old Church Slavonic literacy had the effect of preventing the assimilation of the South Slavs into neighboring Byzantine culture, which promoted the formation of a distinct Bulgarian identity in the Empire. During the first quarter of the 10th century, the ethnonym “Bulgarians” was adopted by the Slavic tribes in most of Macedonia, while their names were abandoned. Significant role in this transformation, played Clement's life work.
Saint Clement of Ohrid was one of the most prolific and important writers in Old Church Slavonic. He is credited with the Panonic Hagiography of Saint Cyril and Saint Methodius. Clement also translated the Flower Triode containing church songs sung from Easter to Pentecost and is believed to be the author of the Holy Service and the Life of St. Clement of Rome, as well as of the oldest service dedicated to St. Cyril and St. Methodius. The invention of the Cyrillic alphabet is also usually ascribed to him although the alphabet is most likely to have been developed at the Preslav Literary School at the beginning of the 10th century (see Cyrillic script).
The first modern Bulgarian university, Sofia University, was named after Clement upon its foundation in 1888. The Macedonian National and University Library, founded on November 23, 1944, also bears his name. The University in Bitola (Republic of Macedonia), established in 1979, is named after Clement, as well as the Bulgarian scientific base, St. Kliment Ohridski on Livingston Island in the South Shetland Islands of Antarctica.
In November 2008, the Macedonian Orthodox Church donated part of Clement's relics to the Bulgarian Orthodox Church as a sign of good will.