Joannes Florentius was the fifth son of the probably more famous Nicolaes a Kempis. Like his father, Joannes Florentius was also a composer and an organist. Between 1670 and 1672, he succeeded to his father’s position as an organist at the St. Michael and Gudula Cathedral in Brussels. Before that, he had a similar position at the ‘Chapel of Our Lady’ Church in Brussels.
His collection of Cantiones Natalitiae for five voices was published in 1657. Similar Christmas carols by the Brussels composers Guillielmus Borremans and Gaspar de Verlit had already been published in 1660. Furthermore, a Kempis published a mass, a sequence Victimae paschalis en twelve sonatas for violin, viola da gamba and double bass. A polychoral Canticle of Zachary has been ascribed to Guillaume a Kempis.