- The Legislative Assembly, or lower house, was created under the Constitution Act 1889 when Western Australia achieved responsible self-government. The number of seats has increased steadily over time, from 30 for the first election, to the current total of 57 seats. Each member is elected to a single-seat constituency with a system of alternate vote known as preferential voting, in a manner similar to the Federal House of Representatives. The leader of the party or coalition with the most seats in the Legislative Assembly after an election is invited to form a government.
- The Legislative Council, or upper house, was initially created as an appointed advisory council to the Governor of Western Australia, accountable to the British government. In 1870, it became a two-thirds elected body, and in 1894 it became a fully elected body upon royal assent of the Constitution Acts Amendment Act 1893 which amended the Constitution Act 1889, which divided the state into provinces which were each represented by three members, elected for six-year terms in staggered biennial elections. The Legislative Council maintained its own electoral roll with different suffrage requirements until 1965, when the rolls and election dates were harmonised with the Legislative Assembly. Since 1989, members have been elected for four-year terms through a preferential system of proportional representation in six regions.
Originally, political parties as organised entities did not exist in Western Australia, with members aligning with individuals such as founding premier Sir John Forrest and George Leake. At the 1901 election, the newly-formed centre-left Labor Party won six of the 50 seats on offer. By 1911, the transition to a two-party system was complete with the emergence of a rival to Labor in the centre-right Liberal Party of Western Australia, which many of the former independents had joined. This entity evolved into the Nationalist Party and eventually into the Liberal Party in 1944. With the exception of the 1996 election, where the Liberal Party won an outright majority of Legislative Assembly seats, the Liberals (and Nationalists before them) have had to rely on coalition agreements with the Country Party of Western Australia, now known as The Nationals Western Australia, to succeed in forming a government. The Country Party have held seats continuously since their emergence at the 1914 election, and during the period from 1933 until 1947 were the second-largest party in Parliament after Labor. Since 1989, with the advent of proportional representation in the Legislative Council, a number of other parties have succeeded in winning seats in that house, including the Greens, Democrats and One Nation.
Two other features of the Western Australian electoral system are worthy of note in interpreting election results. The first is that until the 1974 election, many seats in both houses were uncontested—usually more than one-quarter of all seats on offer. Since 1974, only one seat has been uncontested—that being the seat of East Melville in the 1980 election, when the Labor candidate missed the nomination deadline. The second feature is that seats in metropolitan and rural areas do not contain the same number of electors—as at 30 September 2007, a Member of the Legislative Assembly may represent 28,519 metropolitan voters within the Metropolitan Region Scheme area, or 14,551 country voters, whilst a Legislative Councillor may represent 13,101 Mining and Pastoral voters, 22,354 rural voters or 57,038 metropolitan voters. This is believed to disproportionately favour the Nationals in terms of parliamentary representation.
- de Garis, Brian (1991). "Self-Government and the Emergence of Political Parties 1890-1911". In Black, David. The House on the Hill: A history of the Parliament of Western Australia. Parliament of Western Australia. pp. 81–82. ISBN 0-7309398-3-9.
- Black, David (1981). "The Era of Labor Ascendancy 1924-1947". In Stannage, Tom. A New History of Western Australia. University of Western Australia Press. p. 439. ISBN 0-8556417-0-3.
- Black, p.110.
- Western Australian Electoral Commission (30 September 2007). "September enrolment statistics" (PDF). Retrieved 2008-01-15. Check date values in:
- Green, Antony (17 November 2004). "WA: A Peculiar Electoral System". Australian Broadcasting Corporation. Retrieved 2008-01-19. Check date values in: