"The court rejects the action for annulment," the tribunal said in a press release on Friday, according to Press TV.
In line with the deal, Iranians convicted in Belgium would be allowed to serve their sentences at home and vice versa.
The treaty could lead to the release of Assadollah Assadi, an Iranian diplomat who has been illegally imprisoned in the European country.
In February 2021, a Belgian court sentenced Assadi to 20 years in prison after accusing him of plotting an alleged attack against the terrorist Mujahedin-e Khalq Organization (MKO).
The anti-Iran terrorist cult, the MKO, is responsible for killing over 17,000 Iranians through acts of terror since the 1979 victory of Iran's Islamic Revolution.
Following the sentencing, the Iranian Foreign Ministry strongly condemned the jail term as completely unlawful, in violation of Assadi's diplomatic immunity, and a result of Belgium's falling under the MKO’s influence.
Belgium's Parliament ratified the treaty back last July.
The so-called "National Council of Resistance of Iran (NCRI)," an umbrella group of anti-Iran outfits such as the MKO, has been trying to pose some legal challenges to it, alleging that Assadi should remain in prison.