Iran's Foreign Ministry said the decision was proof of the country’s "righteousness and the violations by the US government".
The case before the ICJ, also known as the World Court, was initially brought by Tehran against Washington in 2016 for allegedly breaching a 1955 friendship treaty.
The 1950s friendship treaty was signed long before Iran's 1979 Islamic Revolution. Washington finally withdrew from the treaty in 2018. Nonetheless, the ICJ ruled that it was in place at the time of the freezing of the assets of Iranian commercial companies and entities.
"The court has concluded the United States violated its obligations under ... the treaty of amity," presiding judge Kirill Gevorgian said. He added that Iran was entitled to compensation and the parties had 24 months to agree on an amount. If that did not work, the court would start new proceedings to determine compensations.