“The Constitutional Court can do nothing but conclude that Mr. Zuma is guilty of the crime of contempt of court,” judge Sisi Khampepe said.
Zuma, 79, is accused of enabling the plunder of state coffers during his nearly nine-year stay in office.
“This kind of recalcitrance and defiance is unlawful and will be punished,” Khampepe said.
“I am left with no option but to commit Mr. Zuma to imprisonment, with the hope that doing so sends an unequivocal message… the rule of law and the administration of justice prevails.”
“The majority judgement orders an unsuspended sentence of imprisonment for a period (of 15 months),” she declared, ordering Zuma to hand himself over within five days.
The commission of inquiry is headed by Deputy Chief Justice Raymond Zondo.
The panel was set up by Zuma himself, under pressure over mounting scandals, shortly before he was ousted in 2018 by the ruling African National Congress.
But he only testified once, in July 2019, before staging a walkout days later and accusing the commission’s Zondo of bias.
He then ignored several invitations to reappear, citing medical reasons and preparations for another corruption trial.
He presented himself again briefly in November but left before questioning, and Zondo asked to ask the Constitutional Court to intervene.
Most of the graft investigated by the commission involve three brothers from a wealthy Indian business family, the Guptas, who won lucrative government contracts and were allegedly even able to choose cabinet ministers.
Zuma is separately facing 16 charges of fraud, graft and racketeering relating to a 1999 purchase of fighter jets, patrol boats and military gear from five European arms firms for 30 billion rand, then the equivalent of nearly $5 billion.
At the time of the purchase, Zuma was president Thabo Mbeki’s deputy.