Trade Minister Tim Groser said NZ was "100 per cent" behind Australia's defence of the law change.
But yesterday's ruling does not make New Zealand's plan to introduce plain packs any easier.
Trade experts point out it is purely a moral victory because it is a constitutional ruling that is not directly relevant to New Zealand. Furthermore, Australia faces legal challenges on two other fronts, they say.
It is being sued for its plain-packet regime by tobacco giant Philip Morris on the grounds that it breaches a free trade treaty with Hong Kong,
Several countries are also suing Australia through the World Trade Organisation (WTO), claiming plain packaging is a barrier to trade and a breach of intellectual property rights.
Chapman Tripp trade expert Daniel Kalderimis said these legal challenges held much more importance here. "If NZ were to be sued in any respect, [an investor-state case] would be a major avenue because we also have a bilateral treaty with Hong Kong."
He said New Zealand's trade agreement with Hong Kong had similar terms to the Australian treaty, but had greater protections on health grounds.
University of Auckland associate dean of law Jane Kelsey said New Zealand could expect a WTO challenge from tobacco-producing countries if it introduced a plain-packaging regime.
If New Zealand lost a WTO dispute, it would feel strong pressure to comply and scrap plain packaging.
The Australian Government promised to fight tooth and nail for plain packets, saying it was willing to spend billions in court.
New Zealand Prime Minister John Key has been more hesitant, saying it is not a "slam-dunk" policy.
Professor Kelsey said that even if the challenges did not have solid legal grounds, they could have a "chilling" effect on other countries which were considering similar measures.
The Ministry of Health has warned the Government that lawsuits from tobacco giants could cost up to $6 million a case to contest, not including compensation if it loses.
There is also some concern that the proposed Trans Pacific Partnership Agreement would provide more direct pathways for United States-based companies to sue the Government.
PLAIN PACKETS: AUSTRALIA
* From December 1, brand names on cigarette packets will remain but colours, fonts, and print size will be standardised.
* Warning labels will be expanded to three-quarters of the front of the pack.
* In New Zealand, submissions can be made on plain packaging up to October 5.