[3][4] In 1619, he gave the governorship of Picardy to Louis XIII's favorite, Charles d'Albert, duc de Luynes, obtaining in exchange that of Normandy.

[5] In the summer of 1620, he joined the revolt of Marie de Medici,[6] but the Parliament of Rouen and the city of Dieppe, which he besieged, remained loyal to the king.

Longueville headed the French delegation in the talks that led to the Treaty of Westphalia which ended the Thirty Years War (1648).

[8] In his role as sovereign prince of Neuchâtel, and acting as antagonist of the Habsburg power rather than as liberal benefactor, he succeeded in obtaining formal exemption from the Holy Roman Empire for all cantons and associates of the Swiss Confederacy.

After the Peace of Rueil (11 March 1649) had ended the first phase of the civil war, Mazarin's sudden arrest of the Grand Condé, his brother the prince de Conti and their brother-in-law the duc de Longueville, on 14 January 1650 precipitated the next phase of the Fronde, the Fronde des nobles.