This chapel was built in 1690 for the de la Tour and Tassis family. The portal shows Faith and Hope, with Saint Marcou as a Benedictine in the centre. The openwork doors have magnificent bronze spindles with a baroque style The interior is entirely in polychrome wood that imitates marble. It is the best preserved example of such Baroque decor in Belgium. Several of the marbles have been identified. This chapel, separated into two parts, follows the layout of the funeral chapel of Sainte Ursule.

The two chapels are crowned with a dome and a lantern. In the first, chapel, there are pretty wooden statues of Saint Helena, mother of Emperor Constantine, of Saint Sebastian, the Roman centurion who was martyred under Emperor Diocletian, of Saint Anthony the Hermit, who lived alone in the desert of Egypt, and of Saint John the Baptist, who announced the Messiah. The decoration of the second higher chapel is in the late Baroque style with magnificent interlacing of acanthus leaves surrounding niches for relics. It contains numerous reliquaries – a true passion of – the princes de la Tour and Tassis In front of the altar, s an antependium in Mechelen leather.

Above the altar, is a painting of Saint Marcou addressing the destitute and infirm. The artist is unknown. Higher still, above the painting on a gilded base, is the bust of Saint Marcou. He lived in the 6th century. After the death of his parents, he gave all his possessions to the poor and retired to Normandy. There, he was ordained a priest and had the power to cure scrofula (the old name for fistulous tubercular lymph nodes) by the laying of hands. This chapel is the counterpart of the sepulchral chapel of the de la Tour and Tassis family, which is to the left of the choir.