The Milan court found Berlusconi, 76, guilty of paying for sex with the underage prostitute and abuse of power for his attempts to cover up the incident, ANSA reported.
The court sentenced Berlusconi to seven years in prison and banned him from holding public office for the rest of his life.
Prosecutors had recommended a six-year sentence in the trial.
Berlusconi and Karima El Mahroug, the Moroccan dancer he is accused of paying for sex before she was 18 years old, both denied the allegation. In Italy, 18 is the legal age for prostitution.
He also is accused of abusing his power to try to hide the affair when he sprung the dancer from police custody after she was arrested for theft. Prosecutors charged he deliberately lied to the police, telling them Mahroug was the granddaughter of Hosni Mubarak, Egypt's president at the time, to have her released from custody May 27, 2010.
Berlusconi argued judges who have ruled against him are part of a leftist plot to oust him from politics.
Berlusconi, a billionaire media and soccer-team owner, admitted giving Mahroug envelopes stuffed with 500-euro notes, but denied having sex with her.