The verdict could not only end the 76-year-old media mogul's 20-year domination of Italian politics but destabilize the three-month-old government of Prime Minister Enrico Letta and send tremors across the euro zone.
The bloc's third largest economy is ruled by an uneasy and fractious coalition of Letta's center-left Democratic Party (PD) and Berlusconi's PDL.
(Read more: Is the net closing in on 'Houdini' Berlusconi?)
The former premier has repeatedly said the government must not fall whatever the verdict but PDL hawks had called for a mass walkout of its ministers and public protests including blocking motorways with demonstrations if he was convicted.
Supporters of the media mogul demonstrated outside his Rome home before the verdict, causing traffic disruption.
A greater threat to the government could come from the faction-ridden PD, many of whose members are already unhappy with ruling in coalition with Berlusconi's party and could rebel following his first definitive conviction.
Because of his age, Berlusconi can do community service or submit to house arrest instead of jail but the sentence is unlikely to take effect until the autumn because of bureaucratic delays.