The deal would see rules on drug patents relaxed
Negotiators have overcome last-minute hitches to reach a deal in Geneva on giving some of the world's poorest countries access to cheap drugs.
World Trade Organisation spokesman Keith Rockwell described the agreement, which settles a long-standing dispute, as "one of the most important decisions" ever taken by the organisation's executive.
The deal could see millions of people around the world receiving medicines to treat killer diseases for the first time.
The 146 members of the WTO had reached agreement in principle late on Thursday, but the decision was delayed following a last-minute hitch.
It is understood that the delay has been caused by up to two dozen countries who had been unhappy about the wording of a 'chairman's statement' agreed by the US, Brazil, India, Kenya and South Africa.
TRADE AND GLOBALISATION
Key issues at the trade talks
The five had previously been at loggerheads over plans to make cheap medicines more widely available.
The principle of allowing developing countries access to cheap versions of key drugs had been agreed at WTO talks almost two years ago but talks had dragged since then on implementing the deal.
Many of the drugs at issue are patented, which means they cannot be copied for 20 years. The WTO talks aimed to ease these rules for some medicines, enabling countries in need to import cheaper versions of essential drugs.
Last December, the United States had blocked a deal on cheap drugs - even though it was backed by all other members of the WTO.
US negotiators said it would allow too many drugs patents to be ignored.
They said the proposed deal would mean that illnesses that are not infectious, such as diabetes and asthma, could also be treated with cheap, generic drugs.
But it was understood that the US would lift its opposition to a deal if WTO states pledged not to abuse the system and to only waive patents "in good faith" and not for commercial gain.
They would also be expected to take all reasonable steps to ensure cheap versions of drugs do not make their way onto markets in rich countries.
The issue has been casting a long shadow over global free trade talks since their launch in 2001.