While they’re both democracies, Australia and the United States of America have very different political systems. Both countries started as British colonies. The US has become a republic though, which means that they have declared independence from a monarch, in this case, the Commonwealth of Nations.

Another difference between the systems is that in the US, the government (president/prime minister and cabinet) seats separately to the parliament, where as in Australia, the government and parliament sit together in the House of Representatives. In Australia, the governor-general can call a federal election anytime but if something happens to the president, the vice-president (treasurer in Australia) has to serve the rest of the term.

The Australian parliament can also take the government out of office or force them to call an election, whereas, in the US, members of the government. can’t be removed by the parliament without impeachment. (removal of government officials without their permission, due to a high crime such as treason)

Also, In the US, voting is not compulsory, this means voting figures are not well balanced and governments can win elections with small percentages. In Australia however, as voting is compulsory, voting results are more balanced as everyone has to vote. Also Australia’s voting age is younger, 18 rather than 21 in the US.

As well as there are differences, there are also similarities. Apart from the obvious, they both have a federal political system. This means there are two levels of government, neither of which can make laws and legislations against eachother.

References
http://www.humanities.mq.edu.au/Ockham/y67xan1.html
http://www.peo.gov.au/students/cl/comparison.html