In disgrace, he was distanced from the court and therefore remained a lieutenant-Général for a very long time, before becoming commander in chief in Roussillon, where he was the originator of great building works and the renewal of the university and played a large rôle in French Freemasonry.

Escaping the carnage that followed the capture of the palais des Tuileries and the September massacres, he was arrested in his château, then guillotined in 1794 at Arras, aged 86 – on the scaffold he cried "I remain faithful to my king, as my ancestors have always been".

Louis XVI, true restorer of the French war and commercial navy, entrusted General de Mailly with the installation of a powerful and fortified port which would finally be able to ensure regular traffic with the whole of Europe, from Spain to Sweden, Scotland to Italy, the Catalan coast to the East, to the Barbary ports, and even as far away as India and the Americas.

Mailly's disgrace did not last long, because he was responsible for going to Spain to compliment the Infanta Marie-Thérèse-Raphaëlle de Bourbon on behalf of the king.

Marshal de Mailly refuses to emigrate; the idea of the king being abandoned in Paris without the clergy and nobility to him is a revolting absurdity.

In 1790, Louis XVI gave him the command of one of four armies decreed by the National Assembly and that of the 14th and 15th military divisions.