Berlusconi was convicted of breaching confidentiality for arranging for a police wiretap concerning a political rival to be leaked and published in a newspaper owned by his brother..
Berlusconi has denied wrongdoing in the case and is likely to appeal and will remain free in the meantime. His lawyer Piero Longo said he was "extremely surprised" at the verdict.
Berlusconi and his brother were ordered to pay 80,000 euros in damages plus 10,000 euros in legal costs to his rival Piero Fassino, who was centre-left leader at the time of the intercepted phone conversation in 2005 between Fassino and the head of insurer Unipol.
In the conversation published in Il Giornale newspaper, Fassino was recorded as saying: "We have a bank!" At the time of the wiretap, Unipol was trying to take over one of Italy's leading banks, Banca Nationale di Lavoro (BNL). Unipol has been historically linked to the left.
Magistrates had ordered the wiretap as part of an investigation into inappropriate interference in the takeover and the transcript.
The publication of the transcript in a national newspaper broke secrecy rules, and Berlusconi was accused of obtaining the transcript from the wiretap company used by magistrates.
Fassino was widely criticised for the remark and his defence had demanded a million euros in damages from the Berlusconis.
Berlusconi is already appealing a one-year jail term handed to him for a tax-fraud conviction and also faces a verdict in a sex trial later in March.
That trial concerns allegations that he paid for sex with an underage prostitute and abused his powers of prime minister to cover up the liaison - punishable with a maxium jail term of 12 years.
Berlusconi is unlikely to serve time in prison and under Italy's legal system a conviction is not definitive until the defendant has exhausted two levels of appeal.
Although Thursday's verdict carries no impact on Berlusconi's eligibility to take part in a new government, it is a another very serious blow to his reputation.
It comes weeks after his right-wing coalition did better than expected in a general election, and is expected to form a major bloc in the next parliament.
Talks on forming a new government are expected to begin next week.
Berlusconi, who has faced over 30 trials, claims he is the target of a vendetta by politically biased prosecutors. He has denied all the accusations against him and has either been acquitted or let off under statutes of limitations.