Thursday's decision marks the first time that Berlusconi, a three-time former prime minister and billionaire media mogul, has been definitively convicted of any crime, as all past rulings against him have been overturned on appeal or charges have expired.

Berlusconi appealed the ruling that was upheld by Italy's appeals court in May, following the original conviction last October. He was found guilty of involvement in a scheme that inflated the price of film distribution rights bought by his Mediaset business empire in order to avoid taxes, with him then pocketing the difference.

On Thursday, the Court of Cassation - Italy's highest court - confirmed the conviction and four-year jail sentence. This would be reduced to one year under an amnesty.

It is unclear whether Berlusconi would actually serve any time in prison, with community service or house arrest a likely option. However, his sentence cannot be imposed until the Senate votes to lift his parliamentary immunity. This could take weeks or months.

The judges ordered a judicial review of the second part of Berlusconi's sentence, a five-year ban from public office. This allows him to remain as a senator and as leader of his center-right People of Freedom Party (PDL) for the moment.

The 76-year-old has continually denied the charges and says he has been unjustly victimized by left-wing prosecutors. However, critics say he has used his influence to avoid punishment since he entered the political scene in the early 1990s.

In June, Berlusconi was sentenced to seven years in prison, after being convicted on charges of paying an underage Moroccan teen for sex in 2010, and then abusing his powers by trying to cover up the encounter with phone calls to Milan police officials. He is appealing these convictions.

Thursday's ruling could put the fragile cross-party coalition led by Prime Minister Enrico Letta under strain, even though Berlusconi has pledged his center-right party will continue to support the government.

After winning nearly a third of the vote in Italy's February general election, Berlusconi's party is now an influential member of Letta's coalition.

jr/hc (AFP, AP, Reuters, dpa)