The World Health Organisation hopes the first ever public health treaty will stop the estimated five million annual deaths caused by smoking from doubling by 2020, once it is passed into law by all the 168 countries that have signed up.
"I encourage all countries to become party to the treaty. This can result in millions of lives saved, and that is where the real success of this treaty resides," said WHO Director General Lee Jong Wook.
"Its entry into force is a demonstration of governments' commitment to reduce death and illness from tobacco use," he added.
The WHO regards tobacco as the only legal product that eventually kills half its regular users, fuelling the second leading cause of death in the world.
"This means that out of 1.3 billion smokers, 650 million will die prematurely," it added in a statement.
Tobacco-related ill-health is thought to sap $200 billion from rich and poor countries.
The cost of treating illness due to smoking is estimated to rise to $6.5 billion in China alone, according to the UN's health agency.
Despite three years of strong opposition from tobacco multinationals, as well as governments with substantial tobacco industries or farming, the treaty concluded in 2003 advocates bans on advertising and sponsorship, as well as sales to minors.
The Framework Convention on Tobacco Control also includes public smoking restrictions, larger health warnings on cigarette packs and promotes taxation as a way to cut consumption and fight smuggling.
"Its entry into force is a demonstration of governments' commitment to reduce death and illness from tobacco use"
Lee Jong Wook
Treaty parties must now pass the measures into national law within three to five years, although health officials acknowledged that several countries have already implemented many of them.
Vera Luiza da Costa e Silva, head of the WHO's tobacco-free initiative, said the convention would "leave fewer loopholes for the tobacco industry, which currently finds ways to circumvent national laws".
"The difference for global tobacco control is that countries party to the convention will be able to implement these measures, especially those with cross border implications, in a coordinated and standardised way," she added.
The treaty is expected to have an impact on direct sponsorship for public and sports events.
The McLaren Formula-1 motor racing team on Tuesday announced a major long term sponsorship deal with a whisky firm from August, which could herald the end of its decades-long association with cigarette companies.
A tobacco advertising ban is due to be implemented in the European Union in August.
Anti-tobacco campaigners urged the United States to ratify the treaty. "We are calling on our government to join with the global community in prioritising people's lives over the profits of giant corporations," said Kathryn Mulvey, head of the US-based advocacy group Corporate Accountability International.