A two-party system is a political party system in which two major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term has different meanings. For example, in the United States, the Bahamas, Jamaica, and Zimbabwe, the sense of two-party system describes an arrangement in which all or nearly all elected officials belong to either of the two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from several factors, like "winner takes all" or "first past the post" election systems. The electoral competition is mostly limited to the two major parties.

The Australian Labor Party (ALP), also commonly known as the Labor Party or simply Labor, is the major centre-left political party in Australia and one of two major parties in Australian politics, along with the centre-right Liberal Party of Australia. The party has been in government since being elected at the 2022 federal election, and with political branches in each state and territory, they currently form government in New South Wales, Queensland, South Australia, Victoria, Western Australia, the Australian Capital Territory, and the Northern Territory. As of 2023, Tasmania is the only state or territory where Labor forms the opposition. It is the oldest continuous political party in Australian history, being established on 8 May 1901 at Parliament House, Melbourne, the meeting place of the first federal Parliament.