Crowning four years of turbulent negotiations, WHO's policy-making annual assembly unanimously adopted the accord amid thunderous applause.
"Today, we are acting to save billions of lives and protect people's health for generations to come," said WHO director-general Gro Harlem Brundtland, who made the anti-smoking drive the top priority of her five-year tenure.
"What a wonderful moment in global public health," said New Zealand Health Minister Annette King, adding that around 20 million people had died since the talks began.
The so-called Framework Convention on Tobacco Control provides for a general ban on tobacco advertising and promotion — or simply restrictions in countries like the United States, where a total prohibition would violate the constitution.
It says that health warnings — including pictures such as diseased gums and lungs — should ideally cover at least half the package and encourages governments to clamp down on terms like "low-tar" and "mild" on cigarette packs.
In particular it aims to stop hard-sell tactics aimed at adolescents and strip tobacco of its image as being glamorous and cool. It also provides for tougher international measures against second-hand smoke and cigarette smuggling, and espouses manufacturer liability.
The treaty takes effect after 40 countries have ratified it. Most delegates — including those from the European Union, China and Japan — told Wednesday's assembly that their governments would move to speedy signature and ratification.
The one notable exception was the United States. U.S. Health and Human Services Secretary Tommy Thompson said Washington was "reviewing the text of the convention."
"The United States is not making commitment to sign or ratify," said Judith Wilkinson of the Campaign for Tobacco Free Kids. "They recognized that the rest of world wanted to go forward but didn't say they would join the rest of the world in ratification. It's an incredible missed opportunity."
For months, anti-smoking activists have accused the United States — home to the world's biggest exporter Philip Morris — of trying to undermine the treaty. The text was agreed March 1 over U.S. objections that it did not allow countries to opt out of individual clauses.
Much work now lies ahead in trying to put the terms of the convention into practice, especially in developing countries that have only weak domestic legislation and which are expected to account for 70 percent of the forecast 10 million annual deaths by 2030.
"It is not the happy end of the story but rather the beginning of a new challenge for WHO," said Japan's chief delegate Yoshio Kimura. Japan — which has a controlling stake in Japan Tobacco International — held out against tough provisions until the closing stages of the talks.
Developing countries have been at the fore in pushing for the convention, saying they need protection from tobacco multinationals who have switched their sales drives from saturated Western markets to Asia and Africa.
WHO estimates that nearly 5 million people die each year from smoking-related diseases.