A member will be disqualified if they are found to have been ineligible for election, or become ineligible to sit, because they:
A member will also be disqualified if they:
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.
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, senators were elected for a six-year term, people appointed to a casual vacancy only held office until the earlier of the next election for the House of Representatives or the Senate, at which the vacancy would be filled by the electors of the relevant state. It was also 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 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, and the new senator's term continues until the end of the original senator's term. 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 South Australia 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).
A vacancy may also exist when a Senator resigns or dies after they were re-elected to the Senate but before the start of the next Senate term. This means a vacancy is created in both the current term and the following term that has not yet commenced, creating a constitutional quirk. This happened for the first time on 24 October 2013, a month after the 2013 federal election, when New South Wales Labor Senator Bob Carr resigned from the Senate. Carr's current term was to expire on 30 June 2014, and he was already re-elected to the Senate in the election for the following term starting 1 July 2014. Deborah O'Neill was selected by Labor to fill the casual vacancy, and was appointed by the NSW Parliament on 13 November 2013. In an unprecedented situation where Carr resigned both his current term and the following term, the NSW Government sought legal advice from the Crown Solicitor of New South Wales regarding the tenure of O'Neill's appointment. The Crown Solicitor's advice was that the NSW Parliament could only fill the current vacancy, and would have to wait until July 2014 (start of the new term) to fill the future vacancy. Initially, there were no planned sitting days between July and mid-August 2014, however, a reduced joint sitting of 13 lower house MPs and over 40 Legislative Councillors was held on 2 July 2014 to reappoint O'Neill to the Senate for the new term.
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 (Text). In the event that the Assembly is not in session, the Administrator of the NT (acting on the advice of the territory's executive council) or the Chief Minister of the ACT 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 territory assembly. This procedure is very similar to the procedure for states, albeit under a different legislation or legal document. This process was used in NT for the first and only time on 16 June 1998, when Trish Crossin was chosen by the NT Legislative Assembly to replace Bob Collins, who had resigned from the Senate on 30 March. In the ACT, the 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.
Prior to 1989, different processes were used to appoint territory Senators to casual vacancies. The original Senate (Representation of Territories) Act 1973 was passed in the 1974 joint sitting and took effect on 7 August 1974, allowing the election of two Senators from NT and ACT each. In section 9 of the original act, for NT or ACT casual vacancies, the President of the Senate, or the Governor-General in absence of the President, may issue a writ for the election of a new Senator (i.e. by-election). If there are two casual vacancies in one territory, a writ may be issued for a single election of two new Senators. These provisions were in place until 1980, but they never occurred.
The Senate (Representation of Territories) Act 1973, including Section 9, was amended by the Senate (Representation of Territories) Amendment Act 1980 in May 1980. In the amended Senate (Representation of Territories) Act 1973, NT casual vacancy replacements were to be chosen by the NT Legislative Assembly, the same way as it is currently. The ACT had not gained self-government yet, so the replacement senator was elected by a joint sitting of both houses of the Federal Parliament. This had occurred twice:
In February 1984, these provisions were incorporated into the Commonwealth Electoral Act 1918, as amended by the Commonwealth Electoral Legislation Amendment Act 1983. The ACT gained self-government in 1989, and the Commonwealth Electoral Act 1918 was again amended by the A.C.T. Self-Government (Consequential Provisions) Act 1988 to allow ACT casual vacancy replacements to be chosen by the ACT Legislative Assembly, the same way as it is currently
In accordance with the Commonwealth Electoral Act 1918, the provision of a joint sitting of both houses of the Federal Parliament would still be used to fill a Senate casual vacancy in the representation of any territory other than NT or the ACT), in the event that such a territory ever gained separate Senate representation.
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.
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.