The "People's Tribunal of the Citizens of the World" was started in 2021 by renowned Nuremburg Nazi trial prosecutor Ben Ferencz, Cinema for Peace and Ukrainian rights activist Oleksandra Matviichuk, whose NGO was co-winner of last year's Nobel Peace Prize.
Matviichuk, in an interview with AFP last week urged the United Nations and the European Union to back Kyiv's call for a special tribunal to judge top Russian officials.
The verdict by the court - also calling itself the "Ukraine Tribunal" - comes one year after Moscow's invasion of its neighbor and is largely symbolic as it has no legal powers.
It finds "that there are substantial grounds for the confirmation of an indictment to be issued against President Vladimirovich Putin for more than 1,000 instances of crimes of aggression committed against the territory and the people of Ukraine," judge Zak Yacoob said.
The court urged the "United Nations, the European Union and all the peoples of this world... to ensure that a court with legal powers issue an indictment", to arrest Putin and "put him on trial in an official Ukraine tribunal as soon as possible".
Hearings before the court opened Monday in The Hague, with its organizers saying that although symbolic, it aimed to "close an accountability gap" as there are no current courts able to try crimes of aggression in Ukraine.
These crimes include the invasion or military occupation as well as the bombardment of one country by another, according to the Rome Statute, the founding document of the International Criminal Court, also based in The Hague.
The ICC is currently probing possible war crimes and crimes against humanity committed in Ukraine, but it has no mandate to pursue the broader crime of aggression pertaining specifically to the invasion.
People's court judges said they hoped it "was a step towards prosecution".
"Hopefully we have the authority of moral force and moral persuasion which will take us somewhere," said Yacoob, a former South African Constitutional Court judge and anti-apartheid activist.