With 81.5 percent of votes counted Monday, Ponta's liberal-social democrat alliance won 58.6 percent of the vote in the lower house and 60 percent in the upper chamber, the Financial Times reported.
His victory sets up a strained relationship with the country's center-right president, Traian Basescu, whose alliance trailed with 16.7 percent in the lower house and 16.95 percent in the upper house.
Turnout was 41.6 percent, higher than the last election in 2008, election officials said.
Ponta and Basescu have been rivals since Ponta tried to impeach the president during the summer for allegedly overstepping his powers.
"The election score is very clear ... ," Ponta said. "I hope this day puts an end to a civil war that has been tearing Romanians apart."