Francois Hollande was elected France's first Socialist president in nearly two decades, promising change in Europe after dealing a humiliating defeat to incumbent Nicolas Sarkozy.
The result has major implications not just for France, the eurozone's second-largest economy and a nuclear-armed permanent member of the UN Security Council, but for Europe as it struggles to emerge from its financial crisis.
With only votes from abroad left to count, Hollande had won 51.67 percent of the vote to 48.33 percent for Sarkozy, becoming France's first Socialist president since Francois Mitterrand left office in 1995.
Greeted after his win by a huge throng of supporters in Paris's iconic Place de la Bastille, Hollande hailed his victory as part of a movement rising in Europe against fiscal austerity.
"You are much more than a people who want change. You are already a movement that is rising across all of Europe and maybe the world," he told the cheering masses.
And earlier Sunday evening he promised a crowd in his hometown of Tulle that he would press the European Union to refocus fiscal efforts on growth.
"This is the mission that is now mine: to give the European project a dimension of growth, employment, prosperity -- in short, a future," he said.
"This is what I will say as soon as possible to our European partners and first of all to Germany... We are not just any country on the planet, just any nation in the world, we are France."
Sarkozy conceded defeat and indicated that he intended to step back from frontline politics.
"The French people have made their choice... Francois Hollande is president of France and he must be respected," the outgoing leader told an emotional crowd of supporters.
While Sarkozy stopped short of confirming his retirement, leaders in his right-wing UMP party told AFP he had told them he would not lead them into June parliamentary elections.
Hollande and his team urged supporters to give the Socialists a strong mandate in the two-round parliamentary vote on June 10 and 17.
"There is still much to do in the months to come, first of all to give a majority to the president," Hollande told the crowd in Paris.
Two polls released Sunday showed the Socialists and Sarkozy's right-wing UMP party neck-and-neck ahead of the vote, with 31 percent planning to vote Socialist and 30 percent for the UMP.
During his presidential campaign, Hollande led in opinion polls throughout. winning the April 22 first round with 28.6 percent to Sarkozy's 27.2 percent.
That made the right-winger the first-ever incumbent to be trailing in the first round.
Despite grey skies and rain showers across much of France, turnout was high. The latest interior ministry figures said 81.03 percent of the 46 million eligible voters had turned out.
The election was marked by fears over European Union-imposed austerity and globalisation, and Hollande has said his first foreign meeting will be with German Chancellor Angela Merkel -- the key driver of EU budget policy.
The 57-year-old Socialist has vowed to renegotiate the hard-fought fiscal austerity pact signed by EU leaders in March to make it focus more on growth.
Hollande appeared to be winning over European leaders quickly on Sunday, with some capitals already echoing his call for growth measures.
Germany reached out, with Merkel inviting Hollande to Berlin and her foreign minister vowing to work with Paris on a growth pact.
And Foreign Minister Guido Westerwelle told reporters in Berlin: "We will work together on a growth pact. I am confident the Franco-German friendship will be further deepened."
In Asia however, markets tumbled in reaction both to Hollande's win and the Greek election, where voters deserted a coalition government that pushed through harsh spending cuts in return for an international bailout.
In Tokyo, the euro hit its lowest level in more than three months, changing hands at $1.2964 in morning trade, down from $1.3082 on Friday in New York.
Hollande has said he will move quickly to implement his traditionally Socialist tax-and-spend programme, which includes boosting taxes on the rich, increased state spending and hiring 60,000 teachers.
Sarkozy fought a fierce campaign, saying a victory for Hollande would spark market panic and financial chaos. And in the final days of the race, he stepped up his rhetoric, calling his opponent a "liar" and "slanderer".
But he failed to overcome deep-rooted anger at meagre economic growth and increasing joblessness, and disappointment that he had failed to live up to the promises of his 2007 election.
Sarkozy, 57, was also deeply unpopular on a personal level, with many voters turned off by his flashy "bling bling" lifestyle -- exemplified by his marriage to former supermodel Carla Bruni -- and often aggressive behaviour.
The first round of the election last month saw a record 18 percent score for Marine Le Pen of the far-right, anti-immigrant and anti-Europe National Front.
Sarkozy turned increasingly to the right ahead of the run-off, vowing to restrict immigration and "defend French values". But Le Pen refused to call on her supporters to back him and she cast a blank ballot.
After seeing Merkel, Hollande will set off for a series of international meetings, including a G8 summit in the US on May 18-19 and NATO gathering in Chicago on May 20-21.
In a telephone call, US President Barack Obama invited Hollande for talks before the G8 summit, White House spokesman Jay Carney said.
As well as discussing Europe's economy, Obama is also likely to raise Hollande's pledge to pledge to start bringing 3,300 French soldiers home this year, ending his country's combat role two years earlier than NATO.