Votes were still being counted on Tuesday, but with Berlusconi's victory clear on Monday evening, centre-left leader Walter Veltroni called the 71-year-old to concede defeat.
After two years in opposition, Berlusconi is expected to return to Rome from his home in northern Italy later on Tuesday, although for procedural reasons he is unlikely to be appointed prime minister before early May.
A strong mandate should enable Berlusconi to push reforms through parliament, but many Italians are disillusioned with politics and doubt any government can quickly cure the ills of the European Union's fourth-largest economy.
"The months and years ahead will be difficult and I am preparing a government ready to last five years," Berlusconi told state television in a live phone call on Monday night.
He said his priorities were settling the future of state-controlled Alitalia, which the outgoing administration was struggling to privatise, and clean up a long-standing garbage crisis in Naples.
Berlusconi's pledges include cutting taxes while reducing public debt, liberalising the economy and getting tough on crime. But critics say he failed to carry out pledges to revolutionise Italy when prime minister for seven months from April 1994 and from 2001-2006.
SURPRISE WINNER
Pollsters' projections, based on partial results, gave Berlusconi a 99-seat majority in the 630-member lower house and an advantage of up to 30 seats in the Senate, which has 315 elected and seven lifetime senators.
