 Australia 's electoral system uses preferential voting for all lower house elections with the exception of Tasmania and the ACT which , along with the Senate and most state upper houses , combine it with proportional representation in a system known as the single transferable vote . Voting is compulsory for all enrolled citizens 18 years and over in every jurisdiction , as is enrolment ( with the exception of South Australia ) . The party with majority support in the House of Representatives forms the government and its leader becomes Prime Minister . In cases where no party has majority support , the Governor @-@ General has the constitutional power to appoint the Prime Minister and , if necessary , dismiss one that has lost the confidence of Parliament . 
