The Deputy will understand that transit visas, as with all issues relating to visas, are a matter for the authorities in Australia. At present, the Australian Department of Home Affairs advises that Irish citizens transiting through Australia to another country are not required to apply for a transit visa, provided that their transit time is less than eight hours and they do not intend to clear immigration or leave the airport transit lounge for any reason before boarding their onward flight. However, should the individual in question intend to spend longer than eight hours in Australia during their transit period, or to leave the airport during this time, they will be required to apply for an Australian transit visa.
Information on how to apply for a transit visa is available on the website of the Australian Department for Home Affairs here: https://covid19.homeaffairs.gov.au/transiting-australia.
For additional consular advice or assistance, the individual may also wish to make contact with officials at the Embassy of Ireland in Wellington, who are available to provide support as required.