"Effectively, the accused [Okah] is therefore sentenced to 24 years imprisonment," Judge Neels Claassen said as he handed down sentence.
On 21 January, Okah was found guilty on 13 counts of terrorism, including engaging in terrorist activities, conspiracy to engage in terrorist activities, and delivering, placing, and detonating an explosive device.
The charges related to two car bombs in Abuja, Nigeria, in which 12 people were killed and 36 injured on 1 October 2010, the anniversary of the country's independence.
The second bombing took place in Warri on 15 March 2010 at a post amnesty dialogue meeting. One person was killed and 11 seriously injured.
In both bombings, two car bombs went off minutes apart in both places. The cars were parked in close proximity to each other.
Claassen sentenced Okah to 12 years imprisonment for each of the bombings and 13 years for the threats made to the South African government after his arrest in October 2010.
The 13 years would run concurrently with the 24 years.
In January, during judgment Claassen said the State had proved Okah's guilt beyond a reasonable doubt, and his failure to testify meant the evidence against him remained uncontested.
Okah has denied any involvement, claiming the charges against him were politically motivated.