So far only Russia, Nicaragua and Venezuela have recognised the two breakaway Georgian provinces as independent.
The report also warned that the risk of new confrontation in the region "remains serious".
Last year's five-day war in August killed at least 390 civilians and displaced more than 100,000 people.
Russia and Georgia have both welcomed the findings, with each saying that it vindicated their actions.
Vladimir Chizhov, Moscow's ambassador to the EU, said the report provided "unequivocal confirmation of who started the war - it was Georgia".
"The report is objective on its main point, it concludes that the conflict started with the aggression by Georgia against South Ossetia," Russia's Interfax news agency quoted him as saying.
But Georgia said the report was proof that Russia had invaded Georgia, violating its territorial integrity.
"The allegations of my country have been proven. It was Georgia which came under invasion from another country, in violation of the international law," Salome Samadashvili, Georgia's ambassador to the EU, said.
Matthew Collin, Al Jazeera's correspondent in Tblisi, the Georgian capital, said the government believes Russia built up military forces in Abkhazia and South Ossetia prior to the conflict, in preparation for war in those regions.
"What the Georgians are also stressing very keenly today is that it wasn't Georgia who invaded anothe country's sovereign territory, it was Russia," he said
President under pressure
Heidi Tagliavina, head of the EU fact-finding mission, said it was their view that Georgia triggered the war when it attacked Tskinvali in South Ossetia with heavy artillery on the night of 7 to 8 August.
"None of the explanations given by the Georgian authorities in order to provide some form of legal justification for the attack lend it a valid explanation," she said.
The report is likely to further damage the reputation of Mikheil Saakashvili, the Georgian president, who has withstood calls by the public to resign over the conflict.
It may also undermine the former Soviet nation's hopes of becoming a Nato member.
The report, based on research by 30 European military, legal and history experts, was mandated by the EU last year to investigate the "causes and roots" of the conflict, but not to determine guilt.