The procedure for non-party intervention at the International Court of Justice (ICJ) was historically seldom used. It has, however, recently taken centre stage in the Ukraine v Russia and South Africa v Israel genocide cases. In the wake of mass intervention in Ukraine v Russia, the rules of intervention have been more tightly circumscribed. Following the reforms, it appears likely that fewer intervening states will be permitted to participate in the oral proceedings of South Africa v Israel.

Background and intervention procedure

Under Article 63 of the ICJ Statute, a state that is not party to proceedings has a right to intervene where the construction of a convention to which it is party is in question. Before June 2024, the Rules of the Court did not significantly limit this right. The Court, of course, enjoyed substantive discretion on admissibility, but as a matter of procedure, states could file interventions up until the date fixed for the opening of oral proceedings and still be entitled to oral intervention (Rules of the Court Article 82 and 86(2), pre-reform). Last-minute declarations were procedurally admissible as of right.

Article 82 went even further, allowing declarations after the opening of oral proceedings in “exceptional circumstances”. The right of an intervening state to be heard in oral proceedings was, by any metric, procedurally expansive.

Mass intervention in Ukraine v Russia

This procedure was used to full effect in the “tsunami” of oral interventions in Ukraine v Russia. The thirty-one admissible interventions were unprecedented in number, and the intervenors’ political support for Ukraine was clear: they were overwhelmingly signatories to a Joint Statement welcoming Ukraine’s application, and their interventions may have been prepared collaboratively. Under the old procedure, the Ukraine v Russia interventions were heard at length by the Court in a powerful moment of international solidarity.

However, the interventions also went beyond the construction of the Genocide Convention. Russia objected that the intervenors in fact became de facto co-applicants in the proceedings. While the submission of abuse of process was rejected, Vice President Gevorgian voted in favour of admitting the declarations only on the basis that there was no discretion not to do so where the procedural requirements had been met. He raised concerns that the “scope of what is permissible under Article 63” was being circumvented [1].

Reform of the intervention procedure

In the wake of Ukraine v Russia, the intervention procedure was substantially reformed and Article 63 more tightly circumscribed. In particular:

• Declarations of intervention must now be filed no later than the date of filing of the Counter-Memorial (Rules of the Court Article 82).
• Whether Article 63 interventions will be heard in oral proceedings is now at the discretion of the Court (Rules of the Court Article 86(2)).

In essence, non-parties must not only prepare and file their Article 63 declarations at an earlier stage, but also there is no longer any guarantee that they will be heard in oral proceedings.

Implications and conclusion  

The Court’s new discretion is almost certainly intended to prevent a further incident of political mass intervention. Its full impact will soon be visible in South Africa v Israel, where the trend of numerous interventions has continued. To date, eighteen states maintain their interventions in that case. How many will be heard in oral proceedings, however, remains to be seen. It may be that the Article 63 right is vindicated orally, as the obligation to ensure the correct application of the Genocide Convention is erga omnes partes, as reiterated by the Court in The Gambia v Myanmar.

In light of Ukraine v Russia, however, a somewhat restrictive approach appears more likely. As a matter of procedural rigour, a respondent state should not be compelled to answer a wave of intervenors on issues beyond treaty construction. Further, mass political intervention is not in line with the purpose of Article 63 to promote “unity in the law.” The provision is designed to facilitate uniform jurisprudence as intervening parties are bound by the Court’s interpretation of the relevant treaty.

The growth of non-party intervention could be a welcome signal of trust in international tribunals, particularly where both the number of cases being litigated and states participating at the ICJ is increasing. Where participation rises, however, so too must the Court maintain control of its proceedings.