France's president-elect Francois Hollande is to start work on forming a new government, after telling supporters his victory gave hope of an end to austerity.
Mr Hollande has vowed to rework a deal on government debt in eurozone member-countries to focus on promoting growth.
The Socialist leader won just under 52% of votes in Sunday's run-off election.
Centre-right incumbent Nicolas Sarkozy is the first French president since 1981 not to win a second term. He is set to hand power to Mr Hollande on 15 May.
Mr Hollande must act quickly to reassure other eurozone countries that he is up to the considerable challenge he faces, the BBC reports.
He has called for a renegotiation of a hard-won European treaty on budget discipline championed by German Chancellor Angela Merkel and Mr Sarkozy.
Mrs Merkel has congratulated the president-elect by phone and invited him to Berlin to hold talks soon, but warned the fiscal compact was "not up for grabs".
Mr Hollande is the first Socialist to win the presidency since Francois Mitterrand in the 1980s.
In his victory speech in his stronghold of Tulle in central France he said he would push ahead with his pledge to refocus EU fiscal efforts from austerity to "growth".
"Europe is watching us, austerity can no longer be the only option," he said.
Nicolas Sarkozy, who has been in office since 2007, had promised to reduce France's large budget deficit through spending cuts.
He becomes the latest European leader to be voted out of office amid widespread voter anger at austerity measures triggered by the eurozone debt crisis.
