The much-awaited report into the events in February and March said a number of detained protesters had been tortured.
More than 40 people died in the unrest, which some officials blamed on Iran.
Bahrain has a majority Shia Muslim population and the violence has fuelled anger against the ruling Sunni royal family and political elite.
More than 1,600 people have been arrested during the protests, which have continued sporadically since the peak of the unrest eight months ago.
'No Iran link' The summary of the 500-page report was presented by the Bahrain Independent Commission at King Hamad's palace in Manama on Wednesday.
AnalysisThe report by the Bahrain International Commission of Investigation was much more critical than many here had believed possible. Before it was published, many in the Shia community had dismissed it as a sham, accusing its authors of being bought off by the regime. Now those voices have been silenced by the evidence laid out by Professor Cherif Bassiouni and his team.
The list of accusations is long. The Bahraini government has been found guilty of illegal arrests, forced confessions, unfair trials, and most importantly the systematic use of torture by the police and internal security agencies.
It will all make very uncomfortable reading for the King and his government. But it also represents an opportunity for the King. Professor Bassiouni told me he hopes the King will be able to use the report as a tool to push forward with reform and to isolate, and ultimately remove, hard-liners inside the Sunni royal government.
Prof Cherif said the evidence seen by the commission "did not prove a clear link between the events in Bahrain and Iran".
He also stressed that it was a "unique and historic" event - the first time a state in the region had voluntarily and without international pressure investigated unrest in its own country.
Prof Cherif is a former UN human rights lawyer. The other commission members are all non-Bahrainis.
The inquiry interviewed more than 5,000 people, including hundreds who say they were tortured in prison.
Many detainees were subjected to torture and other forms of physical and psychological abuse while in custody. ”
He promised to reform Bahrain's laws to protect freedom of speech and other basic rights.
"We do not want ever again to see civilians tried anywhere else but in ordinary courts," he said.
The monarch said the report opened "a new page" in Bahrain's history, promising to sack those officials who had abused their power.
If the king acts to change the way the country is run, then the outcome could be positive, the BBC's Rupert Wingfield-Hayes in Bahrain reports.
If not, then more violence is likely to lie ahead, our correspondent says.