From the family of the lords of Coucy in Champagne, he was appointed Queen's Chaplain by Patent of January 28, 1776.

At the moment when the Revolution began, he was the Vicar-General of the Archbishop of Reims, Bishop de La Roche-Aymon.

Based in Guadalajara, he organized a mutual assistance fund between exiles and solicited the financial support of the Spanish upper clergy.

In 1803, on a report from Dupin, Prefect of the Deux-Sèvres, Bonaparte requested the King of Spain to arrest Coucy and he was subsequently imprisoned until 1807, at the instigation of Abbé Émery and Archbishop Fesch.

In 1816, he gave his resignation of the bishopric of La Rochelle to the king and was appointed to the prestigious title of Archbishop of Reims on August 8, 1817, as a reward for his fidelity to the Bourbons.