In 1822 he commenced work as a clerk in an office of the Perran Foundry, owned by the Fox family of Falmouth, a post previously held by his father, John Henwood.

[citation needed] In 1832 Henwood was appointed to the office of assay-master and supervisor of tin in the duchy of Cornwall, a post from which he retired in 1838.

[2] In 1843 he went to take charge of the Gongo Soco mines in Brazil; afterwards he proceeded to India to report on certain metalliferous deposits for the Indian government; and in 1858, impaired in health, he retired and settled at Penzance.

[2] In 1839 a paper entitled "On the Expansive Action of Steam in some of the Pumping Engines on the Cornish Mines", published in the Philosophical Magazine, won him the Telford Medal in silver.

[2] He was concerned about the conditions of slaves, working in mines, and he published a pamphlet on the subject in 1864, reprinted in volume eight (1871) of the Transactions of the Royal Geological Society of Cornwall.