He was a prolific writer and artist and filled 52,000 manuscript pages with notes and sketches concerning all aspects of Indian life, its wildlife, flora and architecture.
Largely based on his notes and sketches, it was subtitled selected and abridged from a series of familiar letters written during seventeen years residence in India: including observations on parts of Africa and South America, and a narrative of occurrences in four India voyages was published in volumes beginning in 1813.
[2] The book remains a valued record of the culture, flora and fauna of India at the time.
Forbes also published a work in 1810 which advocated the conversion of Hindus to Christianity.
The city of Forbesganj in Araria District in the state of Bihar is named after him.