Why Australia has two houses of Parliament

The short answer

Australia has two houses of Parliament

Australia has two houses of Parliament, known as a bicameral system, because of a deliberate compromise reached at Federation in 1901. The House of Representatives represents the people in proportion to population, with electorates of roughly equal size. The Senate represents the states equally, with each original state having the same number of senators regardless of population. This design reflects the tension between the larger colonies, which wanted representation based on population, and the smaller colonies, which feared domination by New South Wales and Victoria and insisted on equal representation in the upper house as a condition of joining the Commonwealth. Most federal legislation must pass both houses to become law, meaning the two chambers act as a check on each other. The House of Representatives is also where government is formed: the party or coalition that commands a majority on the floor of the House forms the executive government, with the Prime Minister always a member of the House.

This is a federal system guide. State constitutions, parliaments and local-government laws can allocate comparable functions differently.

The useful question is not only “what is the rule?” but also “who administers it, which document controls it, and when might it change?” That distinction prevents an accurate general explanation from becoming wrong advice in a particular election, chamber or policy setting.

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The Federation compromise

The structure of the Australian Parliament was settled during the constitutional conventions of the 1890s, where delegates from the six Australian colonies met to design a federal union. The larger colonies of New South Wales and Victoria, with their substantial populations, favoured a parliament where representation was based on population, which would give them the most influence. The smaller colonies of Tasmania, South Australia and Western Australia feared that a purely population-based parliament would leave them permanently outvoted. Queensland, while populous, also had reservations about centralised power. The compromise that emerged, drawing on the model of the United States Congress, was to create two chambers: a lower house representing the people in proportion to population, and an upper house representing the states equally. This bicameral model was incorporated into the Commonwealth of Australia Constitution Act 1900, an Act of the British Parliament that took effect on 1 January 1901. The two-house design was considered essential to securing the agreement of all six colonies to Federation.

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The House of Representatives: the people's house

The House of Representatives is the lower house of the Australian Parliament and is often called the people's house. Section 24 of the Constitution requires that the House be composed of members directly chosen by the people and that the number of members be, as nearly as practicable, twice the number of senators. Each member represents a single electoral division, and the Commonwealth Electoral Act 1918 requires that these divisions contain approximately equal numbers of electors. As of 2026 there are 151 members of the House of Representatives, each serving a term of up to three years. The House is the chamber where government is formed. By convention, the Governor-General commissions as Prime Minister the person who can command the confidence of the majority of the House, and ministers are drawn from the party or coalition that holds that majority. Money bills, which authorise taxation and government spending, must originate in the House of Representatives under section 53 of the Constitution. The government must maintain the confidence of the House to remain in office.

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The Senate: the states' house and house of review

The Senate is the upper house and is designed as both a states' house and a house of review. Section 7 of the Constitution provides that the Senate shall be composed of senators for each state, directly chosen by the people of the state, with each original state having equal representation. Since 1984 each state has elected twelve senators. The Australian Capital Territory and the Northern Territory each elect two senators. Senators serve six-year terms, with half the Senate facing election every three years in a normal electoral cycle, although the Senate can be dissolved in full under the double dissolution procedure in section 57. The Senate reviews legislation passed by the House of Representatives and can amend or reject bills, with the exception of certain money bills. The Senate committee system is a powerful mechanism for scrutinising government activity, including through the estimates process, where senators examine the expenditure proposals of government departments. The Senate's composition often differs from that of the House because it uses proportional representation, which tends to produce a more diverse chamber with significant crossbench representation.

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How the two houses resolve disagreements

When the House of Representatives and the Senate cannot agree on a bill, the Constitution provides two main mechanisms for resolution. Section 57 provides for a double dissolution: if the Senate twice rejects or fails to pass a bill that has passed the House, with an interval of at least three months between each attempt, the Governor-General may dissolve both houses and call a full Senate election, as well as a House election. After the election, if the disagreement persists, the Governor-General may convene a joint sitting of both houses to vote on the bill. Double dissolutions are rare, having occurred seven times in Australian history. The other mechanism is negotiation: the government usually negotiates with the Senate crossbench or the opposition to secure passage of its bills. Between elections, the Senate acts as an institutional check on the government of the day, a function that is most visible when no single party or coalition controls the Senate.

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Bicameralism at the state level

Not all Australian states have a bicameral parliament. Queensland abolished its upper house, the Legislative Council, in 1922 and has been unicameral, with only a Legislative Assembly, ever since. The Northern Territory and the Australian Capital Territory are also unicameral. New South Wales, Victoria, South Australia, Western Australia and Tasmania all retain bicameral parliaments with both a lower house and an upper house, known as the Legislative Council. The state upper houses generally serve as houses of review, scrutinising legislation passed by the lower house, though their electoral systems and composition vary. The absence of an upper house in Queensland means that legislation can be passed by a single chamber with no institutional review by a second house, although the parliamentary committee system provides some scrutiny.

Evidence review

Practical significance for voters and law-making

For voters, the two-house system means that every Australian votes in two different electoral contests at each federal election: one for a local member in the House of Representatives, using preferential voting, and one for Senate candidates from the entire state or territory, using proportional representation. The two systems produce different outcomes: the House typically delivers a clear majority to one side of politics, while the Senate more often produces a chamber where negotiation is necessary to pass legislation. For law-making, the requirement that most bills pass both houses means that legislation is subject to two distinct rounds of parliamentary scrutiny, with different political dynamics in each chamber. This is widely regarded as a strength of the Australian system, providing a structural safeguard against the concentration of power in a single chamber and ensuring that a broader range of voices is heard in the legislative process.

Common questions

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