Born around 760, Smaragdus became a monk of Saint Mihiel in the diocese of Verdun. As abbot of his monastery he took part in 816 in the Council of Aachen, at which a single monastic rule, the Rule of Benedict, was imposed on all monasteries in the Carolingian Empire. Knowing the Rule from long experience, Smaragdus wrote a detailed Commentary to introduce it to monastics coming to its full observance for the first time.

In typical Carolingian style, Smaragdus draws on Scripture, the Rule itself, several Fathers of both Church and Desert, as well as on earlier monastic rules which had been collected by Benedict of Aniane in the Concordia Regularum. But Smaragdus did not simply reproduce others' ideas. He evinces a deep devotion to Christ and great reverence for Saint Benedict and his Rule; he emphasizes the need to update the Rule's observances to meet the needs of a different society, period of history, and breed of monk. His ninth-century work, largely the fruit of lectio divina, is essential, in the opinion of the late Jean Leclercq, to understanding the monastic and spiritual life of the Middle Ages; and his insights may yet be found enlightening to scholars and monks of the twenty-first century.