In 1913, Mervart was appointed head of the Indian department at the Museum of Anthropology & Ethnography.
In 1914–1918, he and his wife explored much of the territory of South India and Ceylon, and visited Malaya, Singapore and Indonesia.
As a result of this expedition, Mervart managed to assemble a large and unique collection of artefacts and objects of folk art from all over South and Southeast Asia.
In 1926–1929, Mervart published around 20 scientific works (including two monographs) and numerous articles.
In December 1929, according to other sources (Memorial), on 13 January 1930 he was arrested on trumped-up charges in the Academics' Case, accused of espionage and on 8 August 1931 sentenced to five years of imprisonment by the OGPU Collegium.