"This outstanding victory is an endorsement of the 'Mahinda Chintana' (Mahinda vision)," Rajapakse said in a statement thanking supporters.
"I asked you for a strong parliament that can meet any challenge," he said. "I sincerely thank you for giving me an unprecedented majority that will help make Sri Lanka an example to the rest of the world."
His UPFA secured 117 seats in the 225-member assembly with another 45 seats left to be declared, results released by the Elections Commissioner showed. The main opposition United National Party (UNP) was reduced to 46 seats.
"This is a huge endorsement of the work of the president," Rajapakse's spokesman Chandrapala Liyanage said.
"The party has won parliament very comfortably," Liyanage told AFP, predicting that it would secure at least 24 of the undeclared seats, leaving it just nine seats short of a two-thirds majority.
"No party has ever got this much," he added.Rajapakse called the vote two months ahead of schedule after his re-election at the January presidential polls, which were held after he crushed Tamil Tiger rebels and ended a 37-year-old separatist conflict in May last year.