In 1735, Velbrück was made a prébende de chanoine-tréfoncier at the Cathédrale Saint-Lambert de Liège. A year later he was received onto the cathedral chapter by procuration. He was made archdeacon of Hesbaye, then officer of the Scel des Grâces in 1756. A year later he was put in charge of a diplomatic mission to the court at Vienna. In 1759 he became grand master of the palace and prime minister to John Theodore of Bavaria, then bishop of Liège and the head of a sumptuous court. Velbrück was also made a prébende de chanoine at Munster Cathedral in 1757 and in 1765 Louis XV of France gave him command of the royal abbey of Saint-Nicolas at Cheminon, Champagne. This exceptional diplomatic and ecclesiastical career made him the only possible candidate for bishop of Liège at the 1772 elections for that role.
Prince-bishop of Liège
His reign saw the birth of several social, artistic and intellectual initiatives. As an 'enlightened despot' receptive to the progressive ideas arising in the last decades of France's Ancien Régime, he tried to introduce Enlightenment ideas to the Principality of Liège, but a lack of money or power meant that these projects were not always successful. A certain lethargy and narrowness of vision then reigned in the Principality, preventing any real progress. He made several attempts to combat poverty and class inequality but was unable to make a real difference to the deplorable situation. He tried to make changes in several areas, such as public health by setting up the Hôpital général Saint-Léonard as a place where the needy would be welcomed and assisted, a free midwifery course and establishments to combat disease. Velbrück also reformed education, making it open to all by creating free charity schools for poor children and an Education Plan for the Youth of the Country of Liège. Put in charge of executing the decree for the suppression of the Jesuits in Liège in 1773, he handed over their Collège en Isle over to his clergy in 1786 to use as a seminary. He modernised teaching by giving more importance to physical sciences and mathematics and the human sciences, which provided the students with useful objectives for their critical judgment. He also planned to create a large public library. Velbrück was a great protector of the arts and his actions were essential to the renaissance in arts in the bishopric. In 1774 he launched the construction of a public academy of painting, sculpture and engraving. Finally, his most notable work was the 1779 foundation of the Société littéraire de Liège and the Société d’Emulation, a meeting-place for Liège's intelligentsia and for them to come into contact with foreign scholars – these societies' many activities included presentations of scientific discoveries and artists' and poets' works. It has been claimed later that he was also a freemason, effectively a member of a Liège lodge, the Parfaite Intelligence et l'Etoile Réunies, but proof has never been produced. The Master of this lodge, Dwelshauwers-Dery, wrote in his history of freemasonry in Liège: Après avoir fouillé nombre d'archives inconnues jusqu'ici, je n'ai trouvé aucune preuve que le Prince de Velbrück ait été franc-maçon. This has not been convincingly contradicted since. He was buried in Liège and his mausoleum escaped being destroyed during the Liège Revolution in which his remains, unlike those of his predecessors, were not thrown into a ditch. His restored mausoleum has since 15 June 2000 been in the cloister of the Cathédrale Saint-Paul de Liège. Its epitaph bears witness to the great regard he was held in by the people of the bishopric:
