Former president Jacob Zuma’s "private prosecution" of his successor Cyril Ramaphosa has been declared unlawful and unconstitutional and has been set aside.

The Gauteng High Court in Johannesburg also ordered that Zuma pays Ramaphosa's costs.

Zuma launched his private prosecution in December last year, on the eve of the African National Congress's national elective conference, in which Ramaphosa was competing for the party's leadership, eventually successfully.

Zuma accused Ramaphosa of "being [an] accessory after the fact to crimes committed by, among others, Adv Downer" - alleged breaches of the National Prosecuting Authority (NPA) Act.

Advocate Billy Downer is prosecuting Zuma on behalf of the State for arms deal-related corruption.

Zuma is seeking to privately prosecute Downer and News24 specialist legal writer Karyn Maughan for allegedly violating the Act by sharing court documents - filed by Zuma's lawyers and the State - that contained a sick note from the former president's military doctor.

Zuma argued that Ramaphosa's failure to investigate made him an accessory after the fact.

Ramaphosa subsequently filed an urgent two-part application.

In the first part, he asked for an interdict against Zuma continuing with his purported private prosecution, pending the finalisation of the second part. This interdict was granted in January.

The second part asked the Gauteng High Court in Johannesburg to declare the purported private prosecution unlawful, invalid and unconstitutional and to set it aside.

After arguments were heard in May, the court handed down its judgment on Wednesday.

The judgment reads, "Mr Zuma's private prosecution of Mr Ramaphosa in respect of the charges set out in the summons and grounded on the allegations set out in the summary of facts attached to the summons is interdicted.

"Mr Zuma is bound by s1(c) of the Constitution to respect the rule of law and the supremacy of the Constitution. While he enjoys the right of access to the court and to have any dispute that can be resolved by the application of law decided in a fair public hearing before a court, the content of this right does not extend to an unlawful, unconstitutional and invalid private prosecution process.

"If allowed, such a private prosecution would breach Mr Ramaphosa's right to human dignity, privacy and security of the person. The Applicant has established a clear right on the basis on which he has been found to enjoy standing in this application, to ensure that both Mr Ramaphosa and the office he occupies as President are protected from such constitutional breaches."

Downer and Maughan also brought applications to have the summons Zuma served them with reviewed and set aside.

The KwaZulu-Natal High Court in Pietermaritzburg last month ruled in Maughan and Downer's favour, setting aside the private prosecution.

Zuma will appeal that ruling.