South Africa's government's had opposed its legalisation, arguing the drug was "harmful" to people's health.
"In the case of cultivation of cannabis, the effect of this judgement is to decriminalise the cultivation of cannabis by an adult in a private place for that adult's personal consumption", he said.
It would therefore not be a criminal offence to use or be in possession of cannabis for personal consumption, in a private space.
A court in the Western Cape region ruled in March that a ban on cannabis use by adults at home was unconstitutional, effectively decriminalising it in the province that includes Cape Town.
If the police officer, on reasonable grounds, suspects that the person concerned is in possession of that cannabis for dealing and not for personal consumption, the officer may arrest the person.
"We are looking forward to telling the police to leave us alone now", said Clarke on the decriminalisation of private use.
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He was of the view that the Court would infringe the doctrine of separation of powers if it determined the amount itself.
Today, the Constitutional Court has agreed, effectively making the personal possession, cultivation and use of cannabis at home legal - or at the very least, decriminalised.
It also found it unjustifiable to prevent a person from possessing, purchasing or cultivating cannabis in the privacy of their own homes.
Pro-marijuana activists cheered in the public gallery and chanted "Weed are free now" when the Constitutional Court gave its landmark ruling.
Parliament would have to decide on this, it said.