"I'm going to race to win," Mr Berlusconi told reporters at the practice field for AC Milan, the soccer club he controls.
"And again I'm doing it out of a sense of responsibility."
The 76-year-old media tycoon resigned in 2011 as prime minister as Italy teetered on the edge of a Greek-style debt crisis and he was dogged by a sex-scandal which included allegations he was involved with an underage prostitute.
The announcement he would run in his sixth national election came just two days after his People of Liberty (PDL) party withdrew support for Mario Monti's government, bringing the country close to a snap election a few months short of the natural end of the legislature.
On Saturday, Mr Berlusconi said PDL would pass legislation proposed by Mr Monti's government, including next year's budget package, and that March 10 was an acceptable date for the parliamentary election, confirming the collapse of Mr Monti's government was not imminent.
Mr Berlusconi has repeatedly changed his mind in the last few months on whether he will stand in the election, but he dropped a strong hint on Wednesday he was about to return to the spotlight.
President Giorgio Napolitano asked the former European commissioner Monti to form a government of technocrats after Mr Berlusconi stepped down, with the support of a right-left coalition that includes the PDL.
Mr Monti imposed austerity measures to bring borrowing costs under control. But the higher taxes have weighed on consumer spending and deepened a recession that began in the second half of last year.
Though the euro zone's third-biggest economy is still struggling, Mr Monti has calmed the financial markets and the spread between Italy and German benchmark bonds this week fell to nearly half the level it was when he took over.
Mr Monti, who is a life-appointed Senator, has said he will not stand in next year's vote, but is willing to step in afterward if the result is not clear.