THE federal government's High Court victory against big tobacco should inspire other countries to push ahead with plain packaging laws, Attorney-General Nicola Roxon says.

The win also strengthens Australia's ability to defend itself against challenges already under way in the international arena.

The High Court on Wednesday ruled Labor's world-first plain packaging laws are constitutionally valid.

That means all cigarettes and tobacco products will be sold in drab olive-brown packs from December.

Large graphic health warnings will dominate the packs, while brand names will be written in a small, generic font.

British American Tobacco (BAT), Japan Tobacco International, Philip Morris and Imperial Tobacco Australia will have to pay the commonwealth's legal costs, which the attorney-general says has run into millions of dollars.

"Many other countries around the world ... will take heart from the success of this decision today," she told reporters in Canberra.

"Governments can take on big tobacco and win and it's worth countries looking again at what the next appropriate step is for them."

New Zealand is planning to introduce plain packaging, while the United Kingdom, France, South Africa, China, Norway and Uruguay are considering the measure.

Ms Roxon urged big tobacco to now "accept the decision of the umpire" and drop international efforts to curb plain packaging.

"This (victory) will only improve the government's ability to defend strongly any actions that are taken in international forums," she said.

Phillip Morris Asia is challenging Canberra's laws through the United Nations Commission on International Trade Law.

Ukraine, Honduras and the Dominican Republic have taken a case to the World Trade Organisation, claiming the legislation breaches Australia's commitment under global trade rules.

But experts believe cigarette companies are behind the case - the Ukraine doesn't even trade tobacco with Australia.

The High Court ruled plain packaging did not involve the acquisition of manufacturers' property in the form of brands and logos - a point Ms Roxon said would be "central" to any trade arguments run internationally.

The commonwealth also will argue governments are entitled to implement their own public health measures.

Health Minister Tanya Plibersek dedicated the court victory to big tobacco's victims.

"For anyone who has lost someone to smoking - this one's for you," she told reporters.

In the past, big tobacco has been successful against smaller claimants, but it doesn't have such a good track record against larger litigants it can't outspend.

BAT on Wednesday said it was "extremely disappointed" by the court's decisions.

But spokesman Scott McIntyre insisted the company would "ensure our products comply with the plain packaging requirements and implementation dates".

Cancer Council Australia said big tobacco vigorously opposed plain packaging because it knew that slick design was a powerful tool when it came to encouraging young people to smoke.

"A product that is addictive and kills so many of its users should not be available in bright, branded packs," council chief executive Ian Olver said in a statement.

"We hope other nations follow Australia's lead."

The court's reasons for the judgment will be published later this year.