The Constitutional Court will hear an application on Tuesday on whether the appointment of Menzi Simelane as the country's chief prosecutor was valid.
The challenge has been driven by the Democratic Alliance since 2009.
It contends he is unsuitable for the post of National Director of Public Prosecutions (NDPP) in view of, among other things, comments he made to the Ginwala Commission of Inquiry.
The DA also cites a Public Service Commission recommendation that a disciplinary inquiry be held against Simelane, and an investigation against him by the General Council of the Bar.
At the time of the Ginwala Inquiry in 2008, Simelane said he did not believe the NPA was independent in terms of the Constitution and that it was accountable to the director general of justice - himself at the time.
That inquiry was to determine whether Simelane's predecessor Vusi Pikoli was fit to hold office.
This came after he disagreed with former president Thabo Mbeki's request to hold off on executing an arrest warrant against now jailed national police commissioner Jackie Selebi.
The DA first challenged Simelane's appointment as NDPP in the High Court in Pretoria, but lost.
That court ruled that Simelane had stated he believed in the independence of the NDPP and had taken an oath to protect the Constitution.
Whether he would keep to it, would show in time, the court ruled, adding that President Jacob Zuma's decision to appoint him should stand.
However, on appeal, the Supreme Court of Appeal reversed that decision on December 1, saying both Zuma and Justice Minister Jeff Radebe had made fatal errors in law.
The SCA found that there were pertinent outstanding questions that went directly to Simelane's integrity and that Zuma could not have satisfied himself that Simelane was a “fit and proper” person for the job, as required by the National Prosecuting Act.
The president's decision was found to be irrational, inconsistent with the Constitution and invalid.
The DA applied to the Constitutional Court for confirmation of the order of invalidity.
Zuma placed Simelane on special leave pending the outcome of Tuesday's hearing.
The justice minister and Simelane oppose the confirmation and want to appeal against the findings of the SCA.
The president decided not to oppose the confirmation.
The minister of justice's legal team is expected to argue that it is impossible to conclude that Simelane is not a fit and proper person for the job, that the decision of the SCA interferes with powers granted to the president alone and that the decision violates the separation of powers.
He argues that the decision is not irrational and that allegations of ulterior purpose are unwarranted.
Simelane contends that the president's decision can only be reviewed on narrow grounds of rationality and legality, neither of which has been established, and that the SCA erred in holding that the president's decision had to be reasonable and procedurally fair. - Sapa