As Botanical Collector for the Royal Botanic Gardens at Kew, he accompanied Lieutenant John Oxley on his exploration of the Lachlan Valley (1817) and Captain Phillip Parker King on his surveys of the northwest coast of Australia (1818-22). Later he explored northern parts of New South Wales (Cudgegong River to the Liverpool Plains (1823) and the Darling Downs of Queensland (1826-27).

He made extensive plant collections in both New South Wales and other parts of Australia. His careful observations on the topography, geology, soils, drainage patterns and other environmental features and his perceptive comments on plant distributions, and factors such as fire, are amongst the most useful and reliable ecological information from the early nineteenth century that we have.

He was Colonial Botanist and Superintendent of the Sydney Botanic Garden from March to December 1837.