This page is about casual vacancies in the Australian Parliament.
For other instances of the term "casual vacancy", see Casual vacancy (disambiguation).

In the Parliament of Australia, a casual vacancy arises when a member of either the Senate or the House of Representatives:

  • dies
  • resigns mid-term[1]
  • is expelled from Parliament and their seat is declared vacant,[2]
  • is absent from (fails to attend) the house, without the permission of the house, for two consecutive months of a session,[3] or
  • is disqualified.[4]


The Commonwealth Electoral Act 1918 requires candidates for Parliament to be Australian citizens.[5]

A member will be disqualified if they are found to have been ineligible for election, or become ineligible to sit, because they:

  • are a subject or citizen of a foreign power or under an acknowledgment of allegiance, obedience or adherence to a foreign power[6]
  • are attainted (convicted) of treason
  • have been convicted and are under sentence or subject to be sentenced for an offence punishable by imprisonment for one year or longer under a Commonwealth or State law
  • are an undischarged bankrupt or insolvent
  • hold any office of profit (i.e. income) under the Crown or any pension payable during the pleasure of the Crown out of any Commonwealth revenues,[7] or
  • have any direct or indirect pecuniary interest in any agreement with the Commonwealth Public Service in any way other than as a member in common with other members of an incorporated company consisting of more than 25 persons.[8]

A member will also be disqualified if they:

  • take the benefit, whether by assignment, composition, or otherwise, of any law relating to bankrupt or insolvent debtors[9]
  • directly or indirectly take or agree to take any fee or honorarium for services rendered to the Commonwealth, or for services rendered in the Parliament to any person or State[10]
  • have been convicted of bribery, undue influence or interference with political liberty, or have been found by the Court of Disputed Returns to have committed or attempted to commit bribery or undue influence when a candidate (the disqualification is for two years from the date of the conviction or finding),[11] or
  • are of unsound mind.[12]


A member of the House of Representatives may resign by tendering the resignation to the Speaker, as required by section 37 of the Australian Constitution, or in the absence of the Speaker to the Governor-General. Similarly, a senator would tender the resignation to the President of the Senate or in the absence of the President to the Governor-General, as required by section 19 of the Constitution.

How a casual vacancy is filled

Casual vacancies are handled in different ways, depending on the house concerned.



When a Senate seat representing one of the six states becomes vacant, Section 15 of the Australian Constitution requires the parliament of the relevant state to choose a replacement. This is done in a joint sitting of the upper and lower houses (except for Queensland, which has a unicameral parliament). In the event that the state parliament is not in session, the governor of the state (acting on the advice of the state's executive council) may appoint the replacement, but such an appointment lapses if it is not confirmed by a joint sitting within 14 days after the beginning of the next session of the state parliament.

Prior to 29 July 1977, it was an established convention, but not a constitutional requirement, that the state parliament choose (or the governor appoint) a replacement from the same political party as their predecessor. It had also been the practice for the relevant party to provide a list of suitable names to the state premier, and for the state parliament to make the choice. Before 1946, the conventions were not as firmly established, with ten casual vacancies being filled by someone from a different party. After 1946, however, they were not breached again until 1975 – twice:

  • On 30 June 1975, the Queensland Labor Senator Bertie Milliner died suddenly. The Labor Party gave only one replacement name to the Country Party Queensland Premier Joh Bjelke-Petersen - that of Mal Colston. However, on 3 September, at Bjelke-Petersen's instigation, the Parliament of Queensland appointed Albert Field to the vacancy. Although he had been a member of the Labor Party for 30 years, Field was now openly critical of the Labor government of Gough Whitlam, and he was immediately expelled from the party for accepting the appointment. Field took his seat in the Senate as an independent. However, there were doubts as to his constitutional eligibility to sit at all. Although he had resigned from the Queensland Department of Education the day before he was appointed, the Education Act (Qld) required three weeks' notice of resignation, and it was arguable that he was therefore still in Crown service (this technicality had been ignored many times in the past). The Labor Party immediately challenged Field's appointment in the High Court, and he was on leave from the Senate from 1 October for the remainder of his short-lived term, which ended when the parliament was dissolved on 11 November.[13]

On 21 May 1977, a referendum was held on the question of whether Section 15 of the Constitution should be changed to require future Senate casual vacancies to be filled by a member of the party represented by the former senator at the time of their election, if the state parliament chooses to fill the vacancy. The referendum was passed and came into effect on 29 July 1977. Where a senator had been elected representing a certain party, and changed allegiances to a different party mid-term, and then died or resigned, the replacement senator would be a person representing the first party. This was first implemented when Senator Steele Hall, who at the time of his election represented the Liberal Movement but had later changed to the Liberal Party of Australia, resigned and was replaced by Janine Haines. She represented the Australian Democrats and was chosen because the Liberal Movement had merged with the Democrats.

When a vacancy exists in the Senate as a result of the ineligibility of a person to be elected, as in the 2017 dual citizenship cases, the seat of the disqualified Senator is filled by a countback of the previous Senate election results in the affected State, as was the method used in Re Culleton (No 2) and in the Re Day (No 2).


When a Senate seat representing the Australian Capital Territory (ACT) or the Northern Territory (NT) becomes vacant, the replacement senator is chosen by the ACT Legislative Assembly or the NT Legislative Assembly, under section 44 of the Commonwealth Electoral Act 1918. Where the Assembly is not in session, the choice is made by the Chief Minister of the ACT or the Administrator of the NT, as the case may be.[14] This process was used for the first time on 18 February 2003, when Gary Humphries was chosen by the ACT Legislative Assembly to replace Margaret Reid, who had resigned from the Senate on 14 February.[15]

Prior to the ACT gaining self-government in 1989,[16] ACT and NT casual Senate vacancies were the subject of a different law: section 9 of the Senate (Representation of Territories) Act 1973, as amended by the Senate (Representation of Territories) Amendment Act 1980. Under this provision, the replacement senator was elected by a joint sitting of both houses of the Federal Parliament. This only ever occurred twice:

This provision would still be used to fill a casual vacancy in the representation of any external territory, in the event that such a territory ever gained separate Senate representation.[19]

House of Representatives

Casual vacancies in the House of Representatives are filled by a by-election. There is no constitutional requirement for a by-election to be held within any particular time, or at all. When a general election is expected within a relatively short time, it has often been the practice not to hold a by-election. This has been justified on the grounds that: (a) the electors of the seat in question should not be burdened with voting twice within a short period of time, when their views are hardly likely to change significantly in that time; and (b) the cost of holding a by-election is considerable, and it is ultimately the taxpayers who bear the cost.

If the Speaker considers it appropriate to hold a by-election, he or she consults with the Australian Electoral Commission as to the suitability of various dates, invites comments from the various party leaders about the proposed dates, makes the final choice, and issues the writ.[20]

At least 33 days must elapse between the moment the Speaker issues a writ and the date of a by-election, and the Speaker cannot issue the writ until receipt of a formal letter of resignation. A by-election must take place on a Saturday.

In the event that since the previous general election there has been a re-distribution that has altered the boundaries of the division in question, the boundaries as at the original election still apply, but only those electors enrolled for that division at the time of the by-election are permitted, and required, to vote.

See also


  1. ^ Constitution sections 19 (Senate) and 37 (House of Representatives). The term "resign" is not to be confused with "retire". A resignation is a voluntary decision by a parliamentarian to end their term early, at a time of their own choosing. A retirement is an involuntary act whereby the sitting member chooses to see out their current term but not to contest the next general election, whenever it is held. The choice of the date of that election is not within the control of the member, but of the government.
  2. ^ There has only ever been one such case, that of Hugh Mahon, who was expelled from the House of Representatives in 1920. Under Section 8 of the Parliamentary Privileges Act 1987 (Cth), neither House currently has the power to expel a member. However, since this provision is not in the Constitution but only statutory, the Parliament can amend or repeal it.
  3. ^ Constitution sections 20 (Senate) and 38 (House of Representatives).
  4. ^ Constitution sections 44 and 45.
  5. ^ Commonwealth Electoral Act 1918 (Cth) s 163 Qualifications for nomination.
  6. ^ The expression "foreign power" now includes the United Kingdom, at least since the passage of the Australia Act 1986: Sue v Hill (1999) 99 CLR 462.
  7. ^ Section 44 goes on to exempt ministerial office and military service. All other public servants must resign their position if they wish to stand for election; taking leave, even without pay, is not enough: Sykes v Cleary (1992) 176 CLR 77 (a schoolteacher).
  8. ^ Constitution section 44.
  9. ^ Constitution section 45(ii).
  10. ^ Constitution section 45(iii).
  11. ^ Commonwealth Electoral Act 1918, s 386.
  12. ^ Commonwealth Electoral Act 1918, s 93.
  13. ^ "The Field Affair" Archived 5 November 2005 at the Wayback Machine
  14. ^ Commonwealth Electoral Act 1918, s 44.
  15. ^ Senate Hansard, 3 March 2003, p. 8815 Archived 31 August 2007 at the Wayback Machine
  16. ^ House of Representatives Practice, 5th edition 2005, p 92.
  17. ^ Senate Hansard, 5 May 1981 Archived 8 February 2012 at the Wayback Machine
  18. ^ Rules for Joint Sittings: footnote, p.3 Archived 16 October 2010 at the Wayback Machine, "Archived copy". Archived from the original on 24 May 2011. Retrieved 12 October 2007.CS1 maint: archived copy as title (link)
  19. ^ This seems unlikely to occur, since the populations of the inhabited external Territories are very small. In the 2011 census Archived 24 March 2012 at the Wayback Machine the ordinarily resident population of Norfolk Island—the only other Territory, and the only external Territory, to be self-governing—was less than 1,800 and in decline.
  20. ^ House of Representatives Practice, 5th edition 2005, p 90.