In 1798 he became secretary to Emmanuel Joseph Sieyès; after serving for a while in the army, he turned to literature, producing several light plays.

In 1819 he was appointed procureur-général at Limoges, and in 1821 was returned for Marmande to the Chamber of Deputies, where he supported the ultraroyalist policies of Villèle.

[1] In contact with practical politics his ultra-royalist views were gradually modified in the direction of the Doctrinaires, and on the fall of Villèle he was selected by Charles X to carry out the new policy of compromise.

He succeeded in passing the act abolishing the press censorship, and in persuading the king to sign the ordinances of 16 June 1828 on the Jesuits and the little seminaries.

In March 1830 Martignac voted with the majority for the address protesting against the famous ordinances; but during the revolution that followed he remained true to his legitimist principles.