1870 in Australia
- Premier of New South Wales — John Robertson, until 13 January then Charles Cowper, until 16 December then James Martin
- Premier of Queensland — Charles Lilley, until 3 May then Arthur Hunter Palmer
- Premier of South Australia — Henry Strangways, until 30 May then John Hart
- Premier of Tasmania — James Milne Wilson
- Premier of Victoria — John Alexander MacPherson, until 9 April then James McCulloch
- 3 January — A state flag of Western Australia is adopted.
- 1 February — A state flag of Victoria is adopted, although with no crown like the current flag.
- 22 March — A state flag of Queensland is adopted, with a portrait of Queen Victoria.
- 20 April — A second state flag of New South Wales is adopted, similar to the current flag of Victoria: a crown above the Southern Cross.
- 22 July — A state flag of South Australia is adopted.
- 11 August — Melbourne Town Hall is opened.
Exploration and settlement
Science and technology
- 23 May – Foster Fyans, first mayor of Geelong (b. 1790)
- 25 May – Captain Thunderbolt (real name Fred Ward, born 1836), bushranger
- 24 June – Adam Lindsay Gordon (born 1833), poet
- Parliament of New South Wales, http://parliament.nsw.gov.au/prod/web/common.nsf/key/ResourcesFactspremiers Archived 16 March 2011 at the Wayback Machine
- Parliament of Queensland, http://www.parliament.qld.gov.au/view/historical/records1860.asp?SubArea=officeHolders Archived 11 July 2009 at the Wayback Machine
- Parliament of South Australia, http://www.parliament.sa.gov.au/Members/Ministers/Pages/PremiersofSouthAustralia.aspx
- Parliament of Tasmania, http://www.parliament.tas.gov.au/tpl/datasheets/Premiers_Table.htm
- Parliament of Victoria, http://www.parliament.vic.gov.au/about/people-in-parliament/premier-of-victoria