On returning to England he collaborated with the zoologist John Edward Gray to publish Illustrations of Indian Zoology (1830–1835).

Hardwicke joined the British East India Company army with the Bengal Artillery as a Lieutenant Fireworker on 3 November 1778.

He was wounded at Satyamangalam on 13 September 1790 and was posted as a Company Orderly at Bangalore before moving to Bengal in 1793 to become Adjutant and Quartermaster of Artillery.

Some drawings were also made by his daughter Elizabeth (between 1811 and 1815 – it was her poor health that led Hardwicke to leave India).

[4] The Indian artists employed by Hardwicke are unknown, except for one Goordial, but they were trained and their style was adapted to the demands of technical illustration using watercolours.

The two volume Illustrations of Indian Zoology was published with Hardwicke's financing, containing 202 large hand-coloured plates, but he died before the textual part was produced.