Handing down judgment, Judge Neels Claassen said the State had proved Okah’s guilt beyond a reasonable doubt. He said Okah’s failure to testify meant evidence against him remained uncontested.
Twelve people were killed and 36 injured in the car bombs on October 1, 2010, the anniversary of Nigeria’s independence.
Okah was arrested in Johannesburg the next day.
He apparently leads the Movement for the Emancipation of the Niger Delta, which claimed responsibility for the blasts.
He was found guilty on Monday of engaging in terrorist activities, conspiracy to engage in terrorist activity, and delivering, placing, and detonating an explosive device.
South Africa has tried him as part of its international obligation, as the Nigerian authorities had not applied for his extradition, according to the prosecution.
After the guilty finding, Okah was taken to the court holding cells under heavy police guard.
When his wife became emotional, a friend comforted her, before they left the courtroom.
About 10 police officers were in the court, with another four outside while the case was being heard. The main road in front of the court was also closed.
Sentencing is expected on January 31.
MEND, or the Movement for the Emancipation of the Niger Delta, carried out numerous attacks on oilfields and pipelines across the swampy region, which is home to Africa’s biggest oil and gas industry, until a government amnesty in 2009.
At its peak, the insecurity was costing the OPEC member nation and Africa’s biggest oil producer $1 billion a month in lost revenues, according to the central bank.