page_title: 2018 South Australian state election
section_title: By-elections
hierarchical_section_title: 2018 South Australian state election / Background / By-elections
caption_attribution_description: English: Photograph of Nat Cook MP, the Member for Fisher in the Parliament of South Australia.
context_page_description: The 2018 South Australian state election to elect members to the 54th Parliament of South Australia was held on 17 March 2018. All 47 seats in the House of Assembly or lower house, whose members were elected at the 2014 election, and 11 of 22 seats in the Legislative Council or upper house, last filled at the 2010 election, were contested. The record-16-year-incumbent Australian Labor Party government led by Premier Jay Weatherill was seeking a fifth four-year term, but was defeated by the opposition Liberal Party of Australia, led by Opposition Leader Steven Marshall. Nick Xenophon's new SA Best party unsuccessfully sought to obtain the balance of power.
  Like federal elections, South Australia has compulsory voting, uses full-preference instant-runoff voting for single-member electorates in the lower house and optional preference single transferable voting in the proportionally represented upper house. The election was conducted by the Electoral Commission of South Australia, an independent body answerable to Parliament.
context_section_description: Independent Bob Such  died from a brain tumour on 11 October 2014 which triggered a by-election in Fisher for 6 December. Labor's Nat Cook won the by-election by nine votes with a 7.3 percent two-party swing against the Liberals, resulting in a change from minority to majority government. On a 0.02 percent margin it is the most marginal seat in parliament. Despite this, the Weatherill Labor government kept crossbench MPs Geoff Brock and Martin Hamilton-Smith in cabinet, giving the government a 26 to 21 parliamentary majority. ABC psephologist Antony Green described the by-election as a "very bad result for the Liberal Party in South Australia" both state and federally, and that a fourth term government gaining a seat at a by-election is unprecedented in Australian history.
  Liberal Iain Evans in Davenport resigned from parliament on 30 October 2014 which triggered a 2015 Davenport by-election for 31 January. Liberal Sam Duluk won the seat despite a five percent two-party swing, turning the historically safe seat of Davenport in to a two-party marginal seat for the first time. ABC psephologist Antony Green described it as "another poor result for the South Australian Liberal Party", following the 2014 Fisher by-election which saw Labor go from minority to majority government.
caption: Labor candidate Nat Cook won the traditionally Liberal seat of Fisher at the December 2014 by-election by just 9 votes (Lib 10,275 LAB 10,284) after preferences from a 7.3 percent Liberal to Labor two-party swing, taking Labor from minority to majority government.
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