Di Girolamo resigned in March 2010 after being accused of masterminding the money laundering scam over which, he, Silvio Scaglia, founder of one of Italy's largest internet companies, Fastweb and 54 other suspects were arrested last year.
Judge Massimo Battistini also sentenced another defendant in the scam, businessman Fabio Arigoni, to five years in prison while a third defendant, Franco Pugliese, was jailed for four years and eight months.
Arigoni and Pugliese were ordered to pay repay unspecified sums of money and all three defendants were barred from holding public office for five years.
Arigoni and Di Girolamo are currently under house arrest while Pugliese, alleged to be an associate of the Calabrian mafia or 'Nrangheta, is already behind bars.
Di Girolamo was elected as a senator representing Italians living in German for Italian prime minister Silvio Berlusconi's ruling centre-right People of Freedom party.