In 1639 he met Gassendi in Paris, and became one of his disciples. He was present at the battles of Rocroi, Nördlingen, and at Lerida. For a time he was personally attached to Condé, but offended him by a satirical remark and was deprived of his command in the prince's guards in 1648. During the Fronde, Saint-Évremond was a steady royalist. The duke of Candale (of whom he has left a very severe portrait) gave a command in Guienne to Saint-Évremond, who had reached the grade of "maréchal de camp". He is said to have pocketed 50,000 livres in less than three years from this office. He was one of the numerous victims involved in the fall of Fouquet in 1661. His letter to Marshal Créqui on the Treaty of the Pyrenees, which is said to have been discovered by Colbert's agents at the seizure of Fouquet's papers, seems a very inadequate cause for his disgrace.