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.
[13] 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.
Despite the constitutional change, a party's nomination to replace the casual vacancy does not guarantee that the nominee will be appointed to the Senate by the state parliament.
Under Tasmanian Parliament's rules adopted for joint sittings, "if the votes are equal, the Question shall be resolved in the Negative".
[15] Ray Groom, a Tasmanian Liberal minister, argued: "section 15 of the Constitution clearly states that it is for the Parliament to choose the person to fill the vacancy and not the party.
Deborah O'Neill was selected by Labor to fill the casual vacancy, and was appointed by the NSW Parliament on 13 November 2013.
[26] If the Assembly is not in session, then 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 within 14 days after the beginning of the next session of the territory assembly.
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.
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, if such a territory ever gained separate Senate representation.
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.
[33] For example, the death of three Cabinet ministers in the 1940 Canberra air disaster on 13 August 1940 meant that three by-elections would have been required.
If, since the previous general election, there has been a re-distribution that has altered the boundaries of the division in question, then 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.