Electronic cigarettes can be shown in UK TV adverts from 10 November, the Committee of Advertising Practice says.
Ruling for the first time specifically on e-cigarettes, the CAP said adverts must not target under-18s or non-smokers, and must not show tobacco "in a positive light".
While the advertising of e-cigarettes on TV is currently allowed, the device itself must not appear on screen.
The committee said the new rules would be reviewed after a year.
Advertising of tobacco products is banned in the UK, except in the trade press.
A CAP spokesman said e-cigarettes were previously "caught" by these rules - written before e-cigarettes existed - because they were held and used like cigarettes.
This meant advertising was allowed, but e-cigarettes could not be shown on screen.
Range of views
The rules state that adverts must not:
- be "likely to appeal particularly to people under 18, especially by reflecting or being associated with youth culture"
- encourage non-smokers to use e-cigarettes
- claim e-cigarettes are "safer" or "healthier" than smoking tobacco
- make any health claims without approval from the Medicines and Healthcare Products Regulatory Agency
The CAP said a consultation before the new rules were created took into account a range of views about e-cigarettes and their "potential to re-normalise smoking, as well as the case being made for their public health benefits".
1. On some e-cigarettes, inhalation activates the battery-powered atomiser. Other types are manually switched on.
2. A heating coil inside the atomiser heats liquid nicotine contained in a cartridge.
3. Liquid nicotine becomes vapour and is inhaled. The "smoke" produced is largely water vapour. Many e-cigarettes have an LED light as a cosmetic feature to simulate traditional cigarette glow.
CAP director Shahriar Coupal said: "We've moved quickly to put in place appropriate and clear regulation around e-cigarette advertising.
"While the debate about e-cigarettes continues our commitment is to make sure they are advertised in a responsible way and that children are protected".
E-cigarettes can already be shown in non-TV advertising, and this will continue when the new rules come into force next month.
The CAP writes and maintains UK advertising rules, which are enforced by the Advertising Standards Authority.