Download form 128 from here:
https://immi.homeaffairs.gov.au/citizen ... itizenship
https://immi.homeaffairs.gov.au/form-li ... ms/128.pdf
You'll need to find an Australian to counter sign and certify the documents. That is actually the hardest part but you DO NOT NEED offical notarisation if you can find a "listed person" such as a teacher or bank officer. It processes fairly quickly. About 6 weeks and they communicate via email quite well.
Don't bother dealing with the lazy overpaid bureaucrats at the Australian High Comm on Napier Rd. They're mostly ignorant, stupid and unhelpful and will obstruct you or charge you some ridiculous fee and they may even shop you to their mates in the MHA (I REALLY do not trust them, don't you trust them either). Just post it into the Immi dept at the Sydney office and pay them online (it is AUD265).
Note that if you are renouncing Australian Citizenship because of the parochial, xenophobic, nationalistic and unfair conscription rules in your second country you should consider the following in order to allow yourself to re-apply for Aussie citizenship once you have ORD'd.:
For posterity the following reasons can be used by ex Australian citizens if they seek to re-instate their Australian citizenship (in case immi.gov.au removed the information - taken from https://immi.homeaffairs.gov.au/citizen ... ligibility)
If you apply to renounce citizenship from Australia I STRONGLY recommend you outline at least two of the reasons below in your statement of why you are renouncing AC.
How your Australian citizenship ceased may affect your eligibility (to regain Australian citizenship).
You are eligible to resume citizenship if you:
became a citizen of another country as an adult before 4 April 2002 (this may apply to older former dual citizens of Singapore & Australia!)
gave up or renounced your Australian citizenship so that you can acquire or retain the citizenship of another country (this applies to dual Aussie/Singapore citizens forced to give up Australian citizenship by the Singapore gahmen).
renounced Australian citizenship to avoid significant hardship or detriment (this applies to dual citizens who will lose their bursaries etc if no longer SC or those who risk prison because of national service issues)
your Australian citizenship was revoked as a child when your responsible parent's Australian citizenship ceased (this may apply to some SC / AC children)
were an Australian citizen by registration or naturalisation and your Australian citizenship ceased because you resided outside of Australia and New Guinea continuously for 7 years between 26 January 1948 and 8 October 1958 (N/A)
