But he was then instructed by Giorgio Napolitano, the country's president, to test his majority in parliament to see if he had the support to return to power.
"It was a good vote," Prodi told reporters. "A great margin, but also the debate showed the centre left is much more united than the centre right and that means the government's work will go ahead strongly. We can go forward well."
But Prodi's grip on power remains fragile as he has only a wafer-thin majority in the Senate and will have to guard against coalition defections, especially on foreign policy and finance.