During his time at the Faculty of Law, Thammasat University (then known in English as University of Moral and Political Sciences), he edited a three-volume set of Siamese laws from official manuscripts of the Law Code of 1805 (1166 Chula Sakarat) promulgated in the first reign of the Chakkri dynasty, under the Three Seals. (From left to right the seals are: 1. The Royal Lion of the Minister of the Interior; 2. The Trunked Lion of the Minister of Defence; and 3. The Crystal Lotus of the Minister of the Port.) In 1941, Lingat submitted to the university a thesis on the history of Thai land tenure, later published in 1949. After the outbreak of the Franco-Thai War (October 1940–May 9, 1941) and during the Japanese occupation of Hanoï, Lingat there published another work on Thailand. He worked at several universities in the former French colonies where, among other things, he was named Professor in the faculty of Law in Indo-China in 1941. Returning to Thammasat, he taught in French with translators rendering his instructions into Thai — a post which he held until 1955. In 1961 he left his post at a university in Cambodia to return to France where, until shortly before his death, he taught at the Center for Indian Studies at the University of Paris.