He joined the 31st Regiment of Foot in Bengal, India, where he distinguished himself as a lieutenant, under General George Pollock in the First Anglo-Afghan War, and wrote an account which was considered an authority on the campaign.
He served in the first and second New Zealand Parliaments, representing the Pensioner Settlements electorate consisting of the Auckland suburbs of Howick, Onehunga, Ōtāhuhu, and Panmure.
[1] He also served on the Auckland Provincial Council, representing the Pensioner Settlements electorate from 1855 to 1857.
Greenwood owned extensive properties in Mangarei (Māngere), and built a house there in 1852.
21 Cumberland Terrace, Regent's Park, London on 18 July 1861 aged 42.