Hi Alex, thanks for your question.
The way people vote in Australia has changed a lot over time. The first federal election in 1902 used ‘first-past-the-post’ voting for both the Senate and the House of Representatives. Preferential voting was introduced for the House of Representatives in 1918 when the Commonwealth Electoral Act 1918 was passed by the Parliament. This was due in part to changing political circumstances after World War 1.
It was not until 1948 that proportional representation was introduced to the Senate. This was to encourage a wider range of political parties and/or independents to be elected.
Voting in Australia will continue to change over time. The Australian Electoral Commission is the independent body responsible for conducting federal elections.
More information about the way voting is conducted for the House of Representatives and the Senate can be found here.