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House of Representatives Practice, 6th edition – HTML version

3 - Elections and the electoral system

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Senate elections

Senators are elected on a different basis to Members of the House of Representatives. Key features of Senate elections are:

  • Each State or Territory votes as one electorate.[97] Twelve Senators are chosen for each State and two Senators for each of the Australian Capital Territory and the Northern Territory.
  • Senators are elected by a system of proportional representation which ensures that the proportion of seats won by each party in each State or Territory closely reflects the proportion of the votes gained by that party in that State or Territory.
  • There is an election for half the number of State Senators every third year. It is not necessary for half-Senate elections and elections for the House of Representatives to occur at the same time, although elections for the two Houses are generally held concurrently.
  • Elections for Territory Senators are held concurrently with general elections for the House of Representatives.
  • State Senators serve for six years from the beginning of their term of service (except following a dissolution of the Senate when half of them serve for three years).[98] Territory Senators serve until the day before the poll of the next general election.
  • A Senate casual vacancy is filled by a person chosen by the Parliament of the State concerned or, in relation to the Australian Capital Territory or Northern Territory, by the respective Legislative Assembly. The person chosen fills the vacancy until the end of the former Senator’s term.[99] If there is one available, a person of the same political party[100] as the Senator previously filling the vacant position must be chosen.

For further information on Senate elections see Odgers.


97. Although the Constitution empowers the Parliament to prescribe a Senate electoral system based on divisions within a State or Territory, that has not been done.
98. Constitution, s. 13. The term of service normally starts on 1 July following the election. After a dissolution of the Senate it starts on 1 July preceding the election.
99. Constitution, s. 15; Commonwealth Electoral Act 1918, s. 44. Before the Australian Capital Territory achieved self-government the Senate and the House of Representatives, at a joint sitting, chose the person to fill a casual Senate vacancy in the Territory. Joint sittings for this purpose were held on 5 May 1981 (J 1980–81/227) and 16 February 1988 (J 1987–89/477–8)—for rules adopted for this sitting see Rules for joint sittings. The mechanism of filling a casual Senate vacancy by means of a joint sitting of the Commonwealth Parliament is retained in the case of a vacancy in a Territory other than the ACT or NT (should any gain Senate representation), Commonwealth Electoral Act 1918, s. 44(2A).
100. That is, the party for which the vacating Senator was elected, Constitution, s. 15.