Microsoft founder Gates told a press conference he will donate 125 million dollars toward the campaign, while New York Mayor Bloomberg said he would chip in with 250 million, on top of the 125 million he already committed in 2005.
"Our goal is to support and complement the Bloomberg initiative," Gates said.
The campaign will back strategies to raise taxes on tobacco products, change the image of smoking in society, protect non-smokers from second-hand tobacco smoke and help smokers give up their habit.
There are some results already: Egypt recently raised sharply its taxes on tobacco products, the Philippines banned all tobacco media advertising, while in Brazil and other countries tobacco packaging bears graphic images to discourage sales.
Two of the world's wealthiest people, Bloomberg (with 16 billion dollars to his name) and Gates (58 billion) have for years donated part of their earnings to philanthropic enterprises.
They told reporters that one billion people will die from tobacco-related diseases during this century unless something is done to reduce smoking, which they called an "epidemic."
A world without tobacco, said Bloomberg, "is a world in which people live longer and have happier lives."
Currently one in four adults in the world is a smoker, or about one billion people approximately.
Bloomberg said the smoking population in New York City has dwindled by some 300,000 since he launched his anti-smoking campaign when he took over as mayor in 2005.
Adult smokers in the Big Apple went from 21.6 percent of the population to 16.9 percent from 2002, he said, adding that he expected similar results in the rest of the world, including developing countries.
More than 80 percent of tobacco-related deaths between now and 2030 will occur in low and mid-income countries, the campaign said.
So far, six countries have banned smoking in all public places, including Britain, France, Italy, Ireland, Uruguay and New Zealand.
The mayor said that every year five million people die around the world from tobacco-related diseases, equal to half the population of New York City.