EFF's Kenny Motsamai was among the 54 permanent delegates to the National Council of Provinces (NCOP) that were sworn in in a ceremony presided over by Chief Justice Mogoeng Mogoeng.
Motsamai will be representing Gauteng on the ticket of the EFF.
Before administering the oath to the permanent delegates, Mogoeng said one of the delegates was convicted and out on parole.
He was referring to Motsamai, who served 27 years and 11 months behind bars for the murder of a traffic officer.
Mogoeng said he knew the issue of Motsamai was debated in the Gauteng legislature based on a provision of the Constitution that provided for members to serve in the NCOP, Parliament and legislatures.
The constitutional provision forbids anybody who was sentenced to a term of imprisonment of 12 months without an option of a fine to serve in the NCOP, Parliament and legislatures.
Reading from the Constitution, Mogoeng said the provision was applicable when the Constitution took effect.
"Information at my disposal, the particular delegate was convicted in 1989 and the constitution took effect in 1996.
"So this section seems not to extend or to exclude that delegate," Mogoeng said.
He also said there should be a good reason why the drafters of the Constitution decided to make the provision applicable only after the adoption of the constitution in 1996.
"It is for that reason that I will be administering oath or affirmation because my own understanding of the constitution is that 'after' means 'after'," Mogoeng said to applause.
Motsamai was sentenced in connection with a murder of a traffic officer during a PAC-sanctioned bank robbery in the late 1980s in Rustenburg.
He was 26 years old at the time he was arrested and had just returned from military training.
Motsmai has refused to apologise or show remorse for the killing of the traffic officer.
In July 2018, he joined the EFF and was elected as parliamentarian during the May 8 elections.