Roxburgh began work in the Carnatic region from 1781 and replaced Patrick Russell as the Company Botanist in Madras on April 1789. His early work was on botany as superintendent in the Samalkot garden in the Northern Circars. Here he conducted economic botany experiments. He employed native artists to illustrate plants. He had 700 illustrations by 1790. He then succeeded Patrick Russell (1727–1805) as Naturalist to the Madras Government in April 1789. From 1793, he and Andrew Ross established a garden at Corcondah, where they worked on sugarcane and indigo. He also studied the prospects of introducing sago and other food crops to help alleviate the effect of famine. He was invited to fill the position of Superintendent at the Calcutta Botanical Garden where the death of Colonel Robert Kyd had created a vacancy. He made rapid progress and acquired a good reputation and was later invited by the government of Bengal, to take charge of the Calcutta Botanical gardens from Colonel Robert Kyd in 1793 as Superintendent of the Company garden at Sibpur near Calcutta. A catalogue of the garden was made in 1814 – "Hortus Bengalensis". He was succeeded by Francis Buchanan-Hamilton.