He became a member of the Russian Academy of Sciences in 1909 and presided over the Academy of the History of Material Culture in 1919-1934. He was one of the leading scholars in the history, archaeology and ethnography of the Caucasian peoples; conducted significant excavations in Georgia and Armenia, bringing to light numerous monuments of Old Armenian and Georgian literature. Studying the Georgian language, he formed the Japhetic theory in linguistics. The theory claimed that Japhetic languages, Georgian among them, had existed across Europe before the advent of the Indo-European languages and could be recognized as a foundation over which the Indo-European languages had imposed themselves.
Using this model, Marr attempted to apply the Marxist theory of class struggle to linguistics, arguing that these different strata of language corresponded to different social classes. This was an attempt to extend the Marxist theory of international class-consciousness beyond its original meaning. In 1924, he went even further and proclaimed that all the languages of the world descend from a single proto-language which had consisted of four enigmatic elements sal, ber, yon, rosh. Enjoying support from the Soviet authorities, Marr run the National Library from 1926 until 1930 and the Japhetic Institute of the Academy of Sciences from 1921 until his death. He was elected vice-president of the Soviet Academy of Sciences in 1930. However, in 1950, Joseph Stalin personally criticized Marr’s theory in his work Marxism and Problems of Linguistics, which denounced Marr as anti-Marxist and anti-scientific. Although Marr’s reputation recovered in the 1960s, his Japhetic theory was not revived.