New York City voted Wednesday to ban the sale of cigarettes, e-cigarettes and tobacco to anyone under the age of 21, raising the previous threshold of 18.
Having pioneered years of stringent anti-smoking laws, the city of 8.5 million becomes the largest metropolis to raise the age limit for buying cigarettes so high.
The US federal age requirement for buying cigarettes is 18, which some states previously raised to 19 and in some, smaller communities to 21.
A spokeswoman for New York City council said the proposal was approved by 35 votes to 10.
Mayor Michael Bloomberg, who has to sign the resolution into law, immediately welcomed what he called a key step towards preventing young people from lighting up.
"Tobacco dependence can begin very soon after a young person first tries smoking so it's critical that we stop young people from smoking before they ever start.
"By increasing the smoking age to 21 we will help prevent another generation from the ill health and shorter life expectancy that comes with smoking."
His administration believes raising the legal age for buying cigarettes will reduce the number of smokers aged 18-20 by as much as 55 per cent.
City hall says that from 2002 to 2011, the percentage of adults who smoke fell from 21.5 to 14.8 per cent.
But while the number of public high school student smokers fell more than half between 2001 and 2011, the decline in youth smoking has stalled at 8.5 per cent.
But the ban will be unpopular among those who feel that Bloomberg has over-stepped the line between protecting public health and interfering with personal choice.
In late 2012, he tried to ban super-sized sugary soft drinks on health grounds sparking angry complaints.
A judge blocked the measure in March, calling it arbitrary, although a final appeal is still pending.
Although New York City was exempt, a US judge this month ordered an end to a smoking ban imposed in public parks and beaches across New York state.
New York City in 2002 pioneered a ban on smoking in bars and restaurants that was initially criticized, but since has been adopted in cities across Europe and the West.
Since 2011, it has also been illegal to smoke on public beaches, parks and public swimming pools in New York City, and its cigarette taxes are the highest in the US.
Bloomberg, who steps down on January 1 after 12 years in office, highlighted health as part of his legacy in an interview with Forbes' November 18 issue magazine.
"You want to leave the world a better place for your kids. From a selfish point of view, you want people to think you've done a great job," he was quoted as saying.
"In this city 8.5 million people are living on average 2.5 years longer than they did 12 years ago. Imagine if it went the other direction!"
New York goes to the polls on Tuesday to elect Bloomberg's successor, with Democratic candidate Bill de Blasio enjoying an historic lead in opinion polls.