He especially contributed to the illustration of natural history subjects, particularly birds, and in his watercolor painting he introduced European styles into a traditional scene dominated by votive art.

Raj Man Singh was the first to apply the Western concepts of lighting and perspective, and is credited for the appearance of three-dimensional effects in Nepalese painting.

He came to the attention of Brian Houghton Hodgson, the British Resident stationed in Kathmandu who was also a scholar of the religions, languages, literature, ethnology and zoology of the Himalaya.

Hodgson was looking for an artist to the make watercolor paintings of the birds and mammals he was studying for his collection, and he hired Raj Man Singh to do them.

Under Hodgson's guidance, the traditional artist, used to painting pictures of deities as per ancient texts, mastered the new technique of observing subjects in their natural habitat and making lifelike representations on paper.