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Childhood and early life
McDonnell was born to Thomas McDonnell Sr., an early British merchant and speculator who served a brief term as Additional British Resident, and his wife Anna McDonnell (née Patterson). He was raised first in Sydney, then Horeke, Northland. There he learned to speak Māori and how to use the traditional taiaha weapon. He tried his luck on the Victorian goldfields from 1853 to 1855, then returned to New Zealand where he obtained a post in the Native Land Purchase Department under Alfred Domett in Auckland. After being paid eight months late, McDonnell resigned from that job and went sheepfarming in the Hawkes Bay with his brother William, only to be defrauded by a third party. He returned to Auckland in 1862, and was appointed interpreter to the resident magistrate at Thames, panning for gold on the side.
Retirement from Military
On 9 April 1870, McDonnell married Henrietta Elise Lomax, in Wellington. Together they had four children. He acquired £690 in government grants and £1,400 worth of freehold property at Wanganui, and set up as a Native Land Court interpreter and land agent at Wanganui in 1884. He received the New Zealand Cross on 31 March 1886, and published fragmented memoirs, as well as a fanciful 'Maori history' of the wars.
Thomas McDonnell died on 8 November 1899.
Belich, James. 'McDonnell, Thomas 1831-1833? - 1899'. Dictionary of New Zealand Biography, updated 22 June 2007