1866 in Australia
- Premier of New South Wales – Charles Cowper (until 21 January), then James Martin
- Premier of Queensland – Robert Herbert (until 1 February), then Arthur Macalister (until 20 July), then Robert Herbert (until 7 August) then Arthur Macalister
- Premier of South Australia – John Hart, Sr (until 28 March), then James Boucaut
- Premier of Tasmania – James Whyte (until 24 November), then Sir Richard Dry
- Premier of Victoria – James McCulloch
- 1 February – Arthur Macalister becomes Premier of Queensland
- 19 March – Sister Mary MacKillop founds the Sisters of St Joseph of the Sacred Heart at Penola, South Australia.
- 17 April – The Tariff Bill passes though the Parliament of Victoria; Australia's first protective tariffs become law the following day.
- 20 June – Adelaide's town Hall opens
- 12 July – SS Cawarra was wrecked off Newcastle, only 1 of 61 passengers and crew survive
- 18 July – The passenger vessel Netherby is wrecked off King Island, all 450 on board survived
- 20 July – Arthur Macalister resigns as Premier of Queensland during a bank crisis, he resumes his post on 7 August as the crisis eased
- 15 August – John Manners-Sutton becomes Governor of Victoria
- 8 September – The Blood or bread riots begin as unemployed men attempt to storm government stores; the riots continue to the 10th
- 10 October – Dandenong Market opens in South-East Melbourne.
- 24 October – The Intercolonial Exhibition of Australasia opens in Melbourne.
- 24 November – Richard Dry becomes Premier of Tasmania
- 7 December – John Granville Grenfell, gold commissioner, killed by bushrangers near Narromine
- 11 January – Gustavus Vaughan Brooke, Irish actor (born 1818)
- 3 February – William Haines, Premier of Victoria (born 1810)
- 7 May – Edward Charles Close, New South Wales colonial magistrate (b. 1790)
- 5 June – John McDouall Stuart, explorer (born 1815)
- 25 September – Osmond Gilles, South Australian colonial treasurer (b. 1788)
- Barker, Anthony (1996). What Happened When. St Leonards: Allen & Unwin. ISBN 978-1-86373-986-3.