Until 1975 all members of the Senate were elected to represent the people of the states. In the elections in December 1975 following simultaneous dissolution of the two Houses on 11 November 1975 the Australian Capital Territory and the Northern Territory each elected two senators for the first time.
Legislation for election of territory senators was enacted in the Senate (Representation of Territories) Act 1973. This legislation was based on the Constitution, section 122, which provides that, in relation to territories, the Parliament "may allow the representation of such territory in either House of the Parliament to the extent and on the terms which it thinks fit". The provisions for the representation of the territories in the Senate are now contained in the Commonwealth Electoral Act, ss 40-44.
The legislation was not enacted without controversy. Indeed, it was one of the bills cited as a ground for the simultaneous dissolutions of 1974 and was eventually passed into law at the joint sitting of that year. It was subsequently twice challenged in the High Court, surviving the first challenge by a majority 4 to 3 decision, and the second by a majority of 5 to 2.
The principal issue in dispute was the contention that territory senators would undermine the constitutional basis of the Senate as a house representing the people by states and that territory representation would disrupt the numerical balance between large and small states. Other questions related to the voting rights of territory senators; the effect of territory senators on the nexus between the sizes of the two Houses and on quorums in the Senate; and applicable criteria in determining whether a territory should be represented in the Senate. A full account of the matter is contained in ASP, 6th ed.That edition concluded that "the broadest possible representation of all the people of Australia best serves that [the Senate's] checks and balances role".
Given that each territory's representation is currently limited to two senators, the practice of electing both at the one election by proportional representation preserves the Senate's role as a House which enhances the representative capacity of the Parliament and provides a remedy for the defects in the electoral method used for the House of Representatives. As indicated in Chapter 1, since the 1980 general election all members of the House of Representatives for ACT electorates have usually been members of the Australian Labor Party. Throughout much of this period, one senator has been a member of the ALP, the other senator from the Liberal Party. One-party representation in the House has also been common for the Northern Territory, so that its two senators are also essential to providing that territory with balanced representation.
The writ for election of senators for a territory is issued by the Governor-General and is addressed to the Australian Electoral Officer for that Territory; following declaration of the result of a Senate election in a territory, the writ is returned to the Governor-General.