The brother of Boeremag mastermind Mike du Toit has been found guilty of high treason in the North Gauteng High Court on Friday.
Andre du Toit was linked to the inner circle that would have carried out the plan to overthrow the government.
The 22 right-wingers face numerous charges, including high treason and terrorism.
Mike du Toit was found guilty of high treason on Thursday.
Judge Eben Jordaan accepted that Andre du Toit was present at many of the meetings arranged by his brother, Mike, and that a coup plot was discussed.
He said Andre was also a part of the Boeremag inner circle which would make tactical decisions when their operation started.
The accused claimed to have believed they were involved in a legitimate war against a "racist regime" but Jordaan said they could not have believed that civilian targets, such as a mosque, were legitimate targets.
They denied all the charges at the start of the trial, which included forming an organisation and recruiting others to overthrow the existing government and committing of serious, violent crimes.
They also manufactured explosives on a large-scale and caused a series of bomb explosions, killing one person and causing damage of millions of rands.
In total, 194 witnesses have testified for the State.