Before 1789 he was a cavalry officer, but in that year was returned as deputy to the states general. In the Constituent Assembly he belonged to the section of moderate royalists who sought to set up a constitution on the British model, and his speeches in favour of retaining the right of war and peace in the king's hands and on the organization of the judiciary gained the applause even of his opponents.
Apart from his eloquence, which gave him a place among the finest orators of the Assembly, Cazalès is mainly remembered for a duel fought with Barnave. After the insurrection of August 10, 1792, which led to the downfall of royalty, Cazalès emigrated. He fought in the army of the émigrés against revolutionary France, lived in Switzerland and in England, and did not return to France until 1803. His son, Edmond de Cazalès (fr), wrote philosophical and religious studies.