Head of State – King George IV
Governor of New South Wales – Major-General Sir Thomas Brisbane, advised of his appointment on 3 November 1820, arrives in Sydney on 7 November. His predecessor, Lachlan Macquarie, whose resignation had finally been accepted at the end of 1820 does not leave New South Wales until 12 February 1822.
12 July – Thomas Kendall, Hongi Hika and Waikato arrive back in the Bay of Islands from their trip to England. While in England they have helped to compile a Maori dictionary, met King George IV who gave Hongi a suit of armour, and Hongi has acquired a number of muskets (his primary purpose).
20 July – Grass is sown for the first time in New Zealand, on land cleared from fern at Kerikeri.
5 September – Hongi Hika and 2000 Ngā Puhi, armed with 1000 muskets, lay siege to Mauinaina pā at Tamaki. The pā is taken and the inhabitants massacred.
– John Gare Butler and his family move into the Mission House even though it is still unfinished.
Construction of the Mission House is started.
Late in the year Hongi Hika and Ngā Puhi lay siege to the Ngāti Maru pā at Te Totara (Thames), but after 2 days they make peace with the defenders and withdraw. They return that night and take the pā without difficulty.
Te Rauparaha and Ngāti Toa move south from Kawhia to resettle in Taranaki after several defeats by Waikato and Ngāti Maniapoto.
21 February (in Scotland): James Menzies, Superintendent of Southland Province.
12 July (in England): William Richmond, politician.
10 August (in England): John Turnbull Thomson, engineer and surveyor.
29 August (in Kerikeri): Elizabeth Fairburn (later Elizabeth Colenso), missionary and Bible translator.
10 September (in England): William Jervois, 10th Governor of New Zealand
2 November (in Ireland): George Bowen, 5th Governor of New Zealand.
John Bacot, politician.
(in England): Samuel Bealey, runholder and politician.
(in England): Thomas Brunner, explorer.
(in Scotland): John Cargill, politician.
Oswald Curtis, politician.
George Hunter, politician.
(in England): Charles Kettle, surveyor of Dunedin.
Reader Wood, politician.
(in England): William Montgomery, politician and merchant.
(in Ireland): George O'Brien, painter.
1821 in New Zealand Wikipedia
Other events of 1821
Timeline of New Zealand history