Born in Rennes, Lanjuinais, after a brilliant college career, which made him doctor of laws and a qualified barrister at nineteen, was appointed counsel to the BretonEstates and, in 1775, professor of ecclesiastical law in Rennes. At this period he wrote two important works which, owing to the distracted state of public affairs, remained unpublished, Institutiones juris ecciesiastici and Praelectiones juris ecclesiastici. He had begun his career at the bar by pleading against the droit du colombier, and when he was sent by his fellow-citizens to the Estates-General of 1789 he demanded the abolition of nobility and the substitution of the Royal titleking of the French and the Navarrese for king of France and Navarre, and helped to establish the Civil Constitution of the Clergy. On 7 November 1789, he requested that the ministers not be members of Parliament at the same time. Since the regulation found a majority, he was able to prevent an increase in Mirabeau's power that sought to take over a ministerial post.
Convention and clandestinity
Elected to the National Convention in September 1792, he developed moderate, even reactionary views, becoming one of the fiercest opponents of Montagnards - although he never wavered in his support for the French Republic. He refused to vote for the death of Louis XVI, alleging that the nation had no right to despatch a vanquished prisoner. His daily attacks on The Mountain resulted, on 15 April 1793, in a demand by the Paris Commune for his exclusion from the assembly, but Lanjuinais remained implacable - when the Parisian populace under François Hanriot invaded the Convention on 2 June, he renewed his defiance of the victorious party. Placed under arrest with the Girondists, he escaped to Rennes where he drew up a pamphlet denouncing the Montagnard Constitution under the curious title Le Dernier Crime de Lanjuinais. Pursued by Jean-Baptiste Carrier, who was sent to stamp out resistance in the west, he lay hidden until some time after the outbreak of the Thermidorian Reaction, but he was readmitted to the Convention on 8 March 1795.
His son, Victor Ambroise, vicomte de Lanjuinais, was also a politician, becoming a deputy in 1838. His interests lay chiefly in financial questions and in 1849 he became minister of commerce and agriculture in the cabinet of Odilon Barrot. He wrote a Notice historique sur la vie et les ouvrages du comte de Lanjuinais, which was prefixed to an edition of his fathers Œuvres.