De Smet was born in Ghent, in what was then the County of Flanders in the Austrian Netherlands, on 11 December 1794.
[1] At the age of 25 he became professor of rhetoric at the minor seminary of St Barbara, and shortly afterwards at the diocesan college in Aalst.
While teaching he wrote new textbooks on Belgian history, world geography and Latin rhetoric, adapted to the needs of Catholic education in the United Kingdom of the Netherlands which had come into being in 1815.
De Smet became a polemical writer against the policy, particularly contributing to his friend Adolphe Bartels's Le Catholique des Pays-Bas.
[3] He was also appointed to the Commission royale d'Histoire at its foundation, and was charged with working on the publication of the Corpus Chronicorum Flandriae.