Polling stations are closing in the French presidential run-off between Nicolas Sarkozy and Francois Hollande.
Preliminary estimates from exit polls are expected from 7pm UK time.
Socialist Francois Hollande leads the French presidential election, according to initial projections
Partial official results also showed Mr Hollande ahead of his rival.
With about half of the nationwide votes counted, official results showed Mr Hollande with 50.8% to 49.2% for Mr Sarkozy.
Nicolas Sarkozy has conceded defeat to Francois Hollande in the French president election
"I take responsibility ... for the defeat," Mr Sarkozy said.
Mr Hollande's former partner and the mother of his four children, Segolene Royal, said she has a "feeling of profound joy to see millions and millions of French renew the tie to the left".
Mr Hollande has arrived in the centre of Tulle where he is expected to address the huge crowd.
Mr Hollande vows to bring change to France and says the change starts now.
He says everyone in the country will be treated equally and nobody will be abandoned or discriminated against
France will overcome its challenges and succeed over the next five years, Mr Hollande says
Mr Hollande says he will bring the hope of growth - rather than austerity - to the rest of Europe
The Socialist politician concludes his speech by vowing to be a president for everybody in France - and is met with deafening cheers
Mr Hollande is now on his way to the airport to fly to Paris
Germany's foreign minister Guido Westerwelle congratulated Mr Hollande, saying both countries will be "a stabillisng factor and a motor for the European Union".
Mr Hollande will travel to the US later this month for summits of Nato - where he will announce he is pulling French troops out of Afghanistan by the end of the year - and the G8.
With 75% of the vote counted, official results now show Mr Hollande with 51.1% of the vote compared with Sarkozy's 48.9%, the Interior Ministry said.
"I know I can count on the personal engagement of Francois Hollande to advance European integration," European Commission President Jose Manuel Barroso said.
UK Independence leader Nigel Farage predicted the new Hollande economic approach would split the Franco-German alliance. "Hollande's election is great news" he said. "It will help drive a wedge between Germany and France, the two of the engines of EU integration."
The new French president is expected to be a force for further European integration, despite his determination to reopen the EU's new "fiscal treaty".
EU officials in Brussels believe Mr Hollande will swiftly deploy renewed French clout in the Union to shake up the current carefully-laid economic strategy of tough budget discipline on eurozone economies and enforced austerity on counties needing bailouts.
European Commission president Jose Manuel Barroso has already congratulated the new president, saying: "I know I can count on the personal engagement of Francois Hollande to advance European integration."
Liberal leader in the European Parliament Guy Verhofstadt said former President Sarkozy's stand on the eurozone crisis had been "disappointing and alarming", but Francois Hollande was now promising to "bring his country back into a European dynamic".
That ends our coverage of the 2012 French presidential elections. Thanks for joining us. Au revoir!