2018 South Australian state election

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 Labor Party government led by Premier Jay Weatherill was seeking a fifth four-year term, but was defeated by the opposition Liberal Party, led by opposition leader Steven Marshall.

Nick Xenophon's new SA-Best party unsuccessfully sought to obtain the balance of power in the Lower House. The party came second on primary votes in ten seats; the strongest results were in Chaffey, Finniss, and Hartley, where the party received over 25%. However, SA-Best received 19.3% of the votes in the Upper House, securing two seats and joining The Greens on the crossbench.

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 (ECSA), an independent body answerable to Parliament.