What voting method is used to elect members of the House of Representatives?

Members of the Australian House of Representatives are elected by preferential voting, also called full preferential or instant-runoff voting. Each voter numbers all candidates on the ballot paper from 1 to the number of candidates, indicating an order of preference. The Australian Electoral Commission then counts votes and distributes preferences until a single candidate has more than 50 per cent support.

The count works in stages. All first-preference (number 1) votes are counted first. If no candidate has more than 50 per cent of the formal vote, the candidate with the lowest number of votes is eliminated, and that candidate's ballots are redistributed to the remaining candidates based on each ballot's second preference. The process repeats, with the lowest-polling remaining candidate eliminated and preferences redistributed, until one candidate has more than 50 per cent of the remaining vote and is declared the winner.

Preferential voting has operated in federal elections since 1918. It replaced the first-past-the-post system (where the candidate with the most votes wins, even without a majority) after the 1918 Swan by-election produced a result that satisfied neither major party. The system was designed to allow voters to support their preferred candidate without the risk of 'wasting' a vote on a candidate unlikely to win, since preferences flow to other candidates if the first choice is eliminated.

The system produces several effects. It rewards candidates who have broad appeal beyond a narrow base, since they need to attract preferences to win marginal seats. It supports minor parties and independents by giving voters confidence to support them as a first preference without risking a 'wasted vote'. It produces clear single-member outcomes even in multi-candidate fields. The system is in widespread use in Australian state lower-house elections and is used in some local government and party-internal elections. Voters must number every box for the vote to be formal at federal level, although some state systems use optional preferential voting where only some preferences must be expressed.