His rival and the architect of his downfall spent the day doing what he does best, charming ordinary Italians by celebrating Valentine's Day at Florence's city hall with hundreds of married couples.
Mr Letta planned tendered his resignation to Italian President Giorgio Napolitano who after a few days of consultations is expected to ask the head of Mr Letta's Democratic Party, Florence Mayor Matteo Renzi, to try to form a government.
Mr Renzi, 39, rallied his party's executives to back him in an internal vote of no-confidence against Mr Letta, accusing him of failing to lift Italy out of its economic and political doldrums.
The ousting came as national statistics bureau Istat reported fourth-quarter GDP edged up 0.1%, the first positive growth since mid-2011.
Mr Renzi's backroom mutiny was surprising even by Italian political standards, since he had long insisted he would only gun for the premiership via an election and the popular mandate that would give him.
However, analysts said he clearly saw an opportunity and seized it, even though the risks of it failing are high.
James Walston, professor of politics at the American University of Rome, said: "Enrico Letta was not a bad prime minister but he was not seen as getting things done.
"Renzi promises to get things done. He promises to make the Democratic Party win and that is his biggest quality at the moment."
It remains to be seen how Italy's shifting political alliances will line up for the required vote of confidence in Parliament once Mr Renzi gets the nod from Mr Napolitano and forms a new government.
Mr Renzi spent yesterday basking in victory and opening up Florence's Palazzo Vecchio city hall to couples celebrating their 50th wedding anniversary.