1840 is considered a watershed year in the history of New Zealand: The Treaty of Waitangi is signed, British sovereignty over New Zealand is proclaimed, organised European settlement begins, and Auckland and Wellington are both founded.
6 April — George Clarke is appointed Protector of Aborigines by Governor Hobson.
18 April — The New Zealand Gazette and Britannia Spectator prints its second issue in Britannia, becoming the first newspaper published in New Zealand. The first issue was printed in England the previous year. The paper publishes weekly, changing its name to The New Zealand Gazette and Wellington Spectator a few months later.
21 May — Governor Hobson proclaims British sovereignty over New Zealand.
— First capital established at Okiato, which is renamed Russell.
— Reverend James Watkin, sent by Johnny Jones, arrives at Waikouaiti and starts the first mission in the South Island.
15 June — The New Zealand Advertiser and Bay of Islands Gazette begins publishing in Kororareka. The newspaper publishes its last issue on 10 December 1840. It was suppressed because of anti-government tendencies.
16 June — HMS Herald, Captain Joseph Nias, arrives at Port Underwood with Major Thomas Banbury to obtain signatures from southern chiefs to the Treaty of Waitangi. The final signatures are added the next day. Later in the month the Herald arrives in Stewart Island where Banbury formally takes possession of the island in the name of Queen Victoria.