Magistrate Brian Nemavhidi also convicted Molemo Maarohanye of racing on a public road and driving under the influence of drugs.
Jub Jub smashed his car into a group of pupils in Soweto in 2010, killing four of them and wounding two others.
Family members and schoolchildren cried as the judgement was handed down.
Molemo Maarohanye was one of South Africa’s best-known musicians, but he fell from grace after the crash, the BBC’s Pumza Fihlani in Johannesburg says.
Jub Jub’s co-accused, Themba Tshabalala, was also convicted of the charges.
They were allegedly drag-racing when their vehicles crashed into the children.
They had pleaded not guilty to the charges.
Both had been out on bail since March 2010 – a decision which sparked protests among pupils who demanded their imprisonment.
Magistrate Brian Nemavhidi revoked their bail and remanded them in custody until sentencing on 30 November.
The court room in Soweto, the main black township in Johannesburg, was packed and there were emotional scenes when the verdict was given.
One of the parents fainted and had to be carried out of the court room.
The court ruled that Molemo Maarohanye and Themba Tshabalala were on cocaine and morphine when the accident happened.
The justice department welcomed the ruling, Sapa news agency reports.
“[The conviction] is clear confirmation of justice not only done but manifestly seen to be done,” its spokesman Mthunzi Mhaga is quoted as saying.
“We commend the National Prosecuting Authority’s aggressive stance of charging irresponsible drivers with murder instead of the usual culpable homicide, which usually attracts non-custodial sentences.”
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