How is prime minster chosen?

Answer 1

On winning government, the political party (or a coalition of political parties) chooses one of its own, customarily the Leader of the party, to become Australian Prime Minister.

There is no fixed tenure for the position of Australian Prime Minister and any serving Australian Prime Minister may have his position challenged and removed from him by members of his party or coalition.

To win government a political party or a coalition of political parties must win a majority of the 150 seats in the Federal House of Representatives (the Lower House) of the Australian Parliament.

Each Member of the House of Representatives represents a separate Federal electoral division, constituted in approximately equal numbers of population.

Members of the Federal Government (House of Representatives and Senate), State, Territory and local governments are elected under a preferential system of voting which requires for election a majority of primary votes.

In cases where the primary votes are not enough to constitute a majority, a combination of primary and preferential votes are tallied until a majority of votes is achieved.

Answer 2

Normally the leader of the political party which has won the majority of seats in the House of Commons is the Prime Minister. He or She is invited to Buckingham Palace after a General Election and instructed by the Sovereign (King or Queen to form the next government. Each of the political parties choose one of their members of parliament to be their leader, in some cases after a ballot involving all members of parliament and other members of the party's electoral college. The exact rules for electing the leader varies between the political parties. When a prime minister leaves office, the party in power choose a new leader, who becomes new prime minister until the next general election. He or she does not necessarily have to be elected.