The certification of the votes cast by Italians living overseas, which had been widely expected, was the final check needed to confirm the outcome of the vote in the Senate after appeals courts in Italy's 20 regions completed reviews on contested ballots cast during the April 9-10 elections.
The Senate certification came four days after Italy's top Court of Cassation confirmed that Prodi's coalition had won a razor-thin majority in the lower Chamber of Deputies.
Despite the widely expected confirmation, Silvio Berlusconi, the Italian prime minister, has refused to concede defeat, although he has begun speaking of a Prodi government and the timing of his own "resignation".
Over the past week, regional appeals courts have confirmed preliminary data from the interior ministry that gave Berlusconi's centre-right bloc 155 Senate seats compared with 154 for Prodi's coalition.
On Saturday, the electoral office for the foreign vote, which is part of Rome's court of appeals, confirmed the ministry's preliminary distribution of the six Senate seats chosen by Italians living overseas. The office certified that four went to Prodi's coalition, one to Berlusconi's allies and one to an independent party.