The ruling was a confirmation of a 2017 Western Cape High Court judgment that afforded the applicants the right to use the herb in the privacy of their homes freely.
Deputy Chief Justice Raymond Zondo, delivering the Johannesburg-based Constitutional Court's unanimous verdict, declared the law banning marijuana use in private by adults "is unconstitutional and therefore invalid". "Ultimately, it will be the court that will decide whether the person possessed the cannabis for personal consumption".
Key laws debated in the Western Cape High Court in 2017 were the Drugs Act sections 4 (b) and 5 (b) as well as section 22A of the Medicines Act.
The order makes it clear that only cultivation of marijuana for private use should be allowed, ruling out commercial growth of the drug as has occurred in the USA state of California, for example.
The court accepted medical studies that showed alcohol caused more harm than weed and that there was little data to show that criminalising weed reduced harmful use.
The ruling states laws prohibiting the use of dagga and the possession, purchase and or cultivation of it in private homes and for personal consumption are inconsistent with the Constitution.More news: Rafa Benitez signals change in tactics for Newcastle's home game against Arsenal
Celebrations broke out in the court, which was packed with marijuana advocates and members of South Africa's Rastafarian community.
The ruling makes it clear that "dealing in" cannabis may only occur as "the cultivation of cannabis by an adult in a private place for his or her personal consumption in private".
The official status for dagga is that it is now "decriminalised". The court did not rule on how many grams an adult will be allowed to use or more crucially carry.
He said that a police officer would have to consider all the circumstances, including the quantity of cannabis found in an adult person's possession.
The news comes following claims that Coca-Cola is in "serious talks" with a cannabis production company to make a cannabis-infused drink.