Saakashvili has been under fire from Georgia's fractious opposition who say he led the country into a war it could not possibly win.
His young, Western-backed government has said it was responding to a Russian invasion, a claim Moscow dismissed as absurd.
Russia said it intervened to protect civilians and has since recognised South Ossetia and a second Georgian breakaway region, Abkhazia, as independent states.
"The Georgian leadership managed to halt the Russian military aggression during the August events," the parliamentary commission said. But "serious systematic and personnel failures took place".
It said civilian and military leaders had failed to foresee and prepare for Russian intervention, operations lacked strategy and co-ordination, and there were problems in military communication.
"As a result, there were serious failures in managing military operations," the bipartisan commission said.
The report said a system of reserve forces was "inadequate and even counter-productive".
The country's military chief of staff was dismissed after the war and the defence minister was replaced this month.
Georgia's former ambassador to Russia, vilified in November when he told the commission he believed Tbilisi had been the aggressor, said he struggled to take the findings seriously.
"The conclusions were known from the very beginning, and say nothing about the fault of the Georgian leadership, which together with Russia led us to the catastrophe we are now in," Erosi Kitsmarishvili told Georgian Imedi television.
The commission's report coincided with the publication by the New York Times of a confidential Pentagon assessment of the Georgian military, which identified a severe lack of co-ordination and a tendency to appoint senior military leaders based on personal relationships rather than qualifications.
Many diplomats say Georgia was clearly baited by Russia but that Saakashvili's August 7 assault was bewildering and Tbilisi's standing with its Western allies has been severely tested.
Western governments criticised Russia's response as "disproportionate" but a freeze on European Union and Nato ties with Moscow was reversed just months later.
A Nato official said high-level talks with Russia would resume on Friday with lunch between Jaap de Hoop Scheffer, the military alliance's secretary-general and Dmitry Rogozin, Russia's envoy to Nato.
At talks in Geneva on Thursday, mediators said Georgian and South Ossetian officials had agreed to work to prevent or resolve security incidents around their de facto border where a fragile, EU-brokered ceasefire is frequently tested by accusations of shooting from both sides.