The election was called after the result of the 2013 Australian federal election for the seats was voided by the High Court of Australia, sitting as the Court of Disputed Returns, on 20 February 2014. The election came about as a result of 1,375 ballot papers being lost during an official recount in November 2013. The High Court ruled that because the number of lost ballots far exceeded the margin for the two remaining Senate seats, the only acceptable remedy was to throw out the results and hold a fresh election. This decision set in motion the process of an special election.
The election is unprecedented in Australian federal politics. An election was held in South Australia in 1907 for the election of one senator under a previous electoral system. Half-Senate elections without a corresponding Australian House of Representatives election have occurred several times due to effluxion of time, the last one having been held in 1970.
The sixth and last seat was a close contest between third Liberal candidate Linda Reynolds and second Labor candidate Louise Pratt. Reynolds was ahead in the ABC's detailed count projection, with Antony Green predicting on 10 April "It is clear the Liberals will win the last seat". The result was confirmed by the Electoral Commission on 29 April. The score at the final count was 188,169 to Reynolds versus 176,042 for Pratt, a margin of 12,127. The projected margin on Green's calculator, which treats all votes as above-the-line, was a narrower 8,109.
Senators elected in the 2013 federal election and the WA special election
Des Headland assumed second place on the Palmer United ticket
Anthony Fels switched from lead Katter's Australian Party candidate to lead Mutual Party candidate
Fiona Patten, who was the lead Sex Party candidate in Victoria in 2013, became their lead candidate at the special election
The Socialist Equality Party and Australian Independents contested the 2013 election in Western Australia, but did not contest the special election. The Socialist Alliance, Pirate Party, Voluntary Euthanasia Party, Building Australia Party, Mutual Party, Republican Party and Democratic Labor Party did not contest the 2013 election in WA, but decided to contest the special election.
Sitting members are shown in bold text. Tickets that elected at least one member in 2014 are highlighted in the relevant colour and successful candidates are indicated with an asterisk (*). Candidates marked with ‡ were declared elected after the final count in 2013.
20 February 2014 – The Court of Disputed Returns voids the results of the WA Senate election. Hayne ruled that the margins between Palmer United and the Australian Sports Party for the fifth seat and the Greens and ALP for the sixth seat were far exceeded by the number of missing ballots. Hayne ruled that since the voters who cast those missing ballots had effectively been "prevented from voting", no remedy short of a new election was appropriate.
21 February 2014 – Electoral Commissioner Ed Killesteyn announces his resignation, which will take effect on 4 July 2014.
28 February 2014 – McCusker announced the election date as Saturday 5 April 2014 
13 March 2014 – closing date for nomination of candidates.
The Senate has 76 seats. Forty seats were up for election; six in each of the six states, two for the ACT and two for the Northern Territory. The terms of the four senators from the territories commenced on election day; all other terms take effect on 1 July 2014.
Most Senate votes cast in Western Australia were subject to a formal recount. During the recount it was determined that 1,375 WA Senate ballot papers could not be located. After the final recount the result was duly declared which changed the last two predicted WA Senate spots from Palmer and Labor back to Sports Party and Greens. Mick Keelty, a former AFPCommissioner, was requested by the AEC to investigate the issue of the misplaced ballot papers. On 15 November, the AEC petitioned the High Court, acting as the Court of Disputed Returns, to seek an order from the court that the WA Senate election of all six senators (3 Liberal, 1 Labor, 1 Green, 1 Sports Party) be declared void.
Given the closeness of the margins that favoured the final two declared candidates, the petition is based on the premise that the inability to include 1,370 missing ballot papers in the recount of the WA Senate election means that the election was likely to be affected for the purposes of s 362(3) of the Commonwealth Electoral Act 1918.
— Australian Electoral Commission, 15 November 2013
A record number of candidates stood at the election.Group voting tickets came under scrutiny because multiple candidates were provisionally elected with the vast majority of their 14.3 percent quotas coming from the preferences of other parties across the political spectrum. "Preference whisperer" Glenn Druery organised tight cross-preferencing between many minor parties. The Sports Party's Wayne Dropulich won a Senate seat on a record-low primary vote of 0.2 percent in Western Australia, his party placing coming 21st out of 28 groups on primary votes. The result caused discussion across a range of organisations and parties about whether there should be changes to the GVT system.