The government is to raise the legal minimum age at which tobacco can be bought in England and Wales from 16 to 18 years from October.
The move is designed to cut teenage smoking rates
The move, announced by Public Health Minister Caroline Flint, will follow the introduction of a ban on smoking in public and work places later this year.
The ban comes into place in Wales in April and England three months later.
About 9% of 11 to 15-year-olds smoke and ministers hope the move will reduce this figure.
However, experts warned other measures were also needed.
The government argues that raising the legal age to 18 will make it easier for retailers to spot under-age smokers.
Ministers also believe that bringing the legal age for the purchase of tobacco into line with that of alcohol will reinforce the dangers of smoking to young people.
It will also bring England and Wales into line with Canada, Australia, New Zealand and the US.
A recent survey suggested that only 23% of children aged under 16 who tried to buy tobacco found it difficult to do so.
Evidence shows that nearly 70% of 11 to 15-year-old smokers say they buy their cigarettes from small shops such as newsagents and corner shops.
Ms Flint said: "Smoking is dangerous at any age, but the younger people start, the more likely they are to become life-long smokers and to die early.
"Someone who starts smoking aged 15 is three times more likely to die of cancer due to smoking than someone who starts in their late 20s.
"Buying cigarettes has been too easy for under 16s and this is partly due to retailers selling tobacco to those under the legal age.
"The law change demonstrates our determination to stop this and to reduce the number of teenagers who smoke.
"This, in turn, will reduce the number of people with preventable diseases and the incidence of health inequalities."
The government made the law change after consulting with the public, the retail industry, the NHS, local authorities and other stakeholders.
Paul Ramsden, deputy chief executive of the Trading Standards Institute, backed the change.
He said: "The institute believes that changing the age of sale in line with the age limit on, for example, alcohol sales will help eliminate confusion among retailers."
Dr Vivienne Nathanson, head of science and ethics at the British Medical Association, said far more needed to be done to discourage children from smoking.
"Increasing the age limit to 18 would be a step in the right direction.
"However, the new limit is only going to be effective if it is properly enforced and part of a broad set of actions designed to discourage young people from starting to smoke."
Dr Nathanson called for more targeted smoking cessation programmes and action to tackle the way that the entertainment industry still portrayed smoking as a cool thing to do.
James Lowman, a spokesman for the Association of Convenience Stores, expressed concern that shop owners could face abusive behaviour if they refused to sell tobacco to young people who had previously been legally able to buy it.
"The government needs to dedicate real resources to public education to prevent this happening.
"Customers need to know they may be asked to prove their age when buying a restricted product like tobacco."