PARIS (Reuters) - French President Francois Hollande's Socialists won a resounding parliamentary majority on Sunday, strengthening his hand as he presses euro zone paymaster Germany to support debt-laden states weighed down by austerity cuts and ailing banks.
The Socialist Party and its affiliates secured 307 seats in the parliamentary election runoff, according to the final count for mainland France, comfortably more than the 289 needed for a majority in the 577-seat National Assembly.
The left-wing triumph means Hollande, elected in May, won't need to rely on the environmentalist Greens, who won 16 seats, or the Communist-dominated Left Front, with 10 deputies, to pass laws. The centre-left already controls the upper house of parliament, the Senate.
"This gives power and a backbone to the government," said Finance Minister Pierre Moscovici, calling the result a vote of confidence in Hollande's government that would enable it to forge ahead with its economic and euro zone policies.
"Europe's future is at stake in the weeks ahead," he said.
The mainstream conservatives, who oppose Hollande's plans to raise taxes on the rich, won 224 seats.
The far-right achieved a breakthrough, winning three seats and giving the National Front a voice in parliament for the first time since the mid-1980s, after an anti-euro presidential campaign by party leader Marine Le Pen struck a chord in a nation struggling with 10 percent unemployment.
Le Pen narrowly lost her race in a working-class northern town, but her 22-year-old niece, Marion Marechal Le Pen, granddaughter of the anti-immigrant party's founder Jean-Marie Le Pen, was elected in the southern town of Carpentras. Lawyer Gilbert Collard, a non-member who was chairman of Marine Le Pen's support committee, and estranged former party member Jacques Bompard won the other two seats in the south.
The leftward swing gives the Socialists more power than they have ever held as Hollande pushes for new tools to stimulate growth in the sickly euro zone and a European banking union that would protect depositors and states if banks fail.
Political turmoil in Greece, where parties that support the country's international bailout were heading for a slim win on Sunday that leaves many problems unresolved, is piling pressure on Europe's leaders to act to contain the bloc's debt crisis at a summit later this month.
Sunday's victory may help Hollande secure parliamentary backing for steps towards a euro zone fiscal union that Berlin is demanding as a condition for agreeing to his push for a growth pact and reforms to improve financial stability.
"It's a much bigger majority than expected," said political analyst Mariette Sineau at the CEVIPOF institute. "It can only reinforce Hollande's position internationally rather than having a weak majority and being hostage to the Greens and Left Front."
The Socialist leader flies to Mexico on Monday for a Group of 20 summit that will be dominated by the euro zone's woes as a rift with the bloc's paymaster Germany over how to resolve the crisis has sparked a rare public squabble.
Hollande, a pro-European social democrat, has broken with a Franco-German power duopoly established under his predecessor Nicolas Sarkozy and is siding with southern euro zone states, calling for more flexibility on deficit targets.
He also wants a European banking union giving the European Central Bank power to supervise cross-border banks, with a joint deposit guarantee and a resolution fund, intended to ensure that bank collapses hit shareholders before taxpayers.
With the right now severely weakened, Hollande's strong hand will be a boon as he readies a wave of legislation for the weeks ahead to raise taxes in line with his tax-and-spend program and ratify a European Union fiscal discipline pact.
As well as avoiding dependence on Eurosceptical or conservative lawmakers, Sunday's win will leave Hollande's mainly social democratic and pro-Europe cabinet intact.
All senior ministers, including Moscovici and Prime Minister Jean-Marc Ayrault, won their parliamentary races.
Ayrault said the government would throw its energy into bolstering public finances, stimulating growth and bringing down unemployment, in the euro zone as well as France. "The goal is to shift Europe towards growth and protect the euro zone from speculation. The task before us is immense," he said.
Hollande, who can count on the backing of his Greens allies in the lower house, will need every parliament vote he can get if a public finance audit due by end-June shows that he must slow down his spending promises to meet France's deficit goals.
One key supporter, his former companion Segolene Royal, who ran unsuccessfully for the presidency in 2007, was beaten on Sunday in the western city of La Rochelle by a left-wing rebel backed by Hollande's current partner, Valerie Trierweiler.
Royal's defeat, making her ineligible for a cabinet post, creates a headache for Hollande, who will need to find a face-saving role for her, especially after a tweet by Trierweiler backing her rival set off a media firestorm.
Another big loser was centrist Francois Bayrou who was punished by centre-right voters for having thrown his support behind Hollande at the last minute. Bayrou lost a seat he had held since 1986, leaving the political centre virtually devoid of a voice after his third presidential bid ended in a crushing fifth place finish in April.
Hollande will still have to work to keep his party united and rally Eurosceptics among the Socialists behind economic and European policies that may be unpopular with the public, such as Germany's demand for deeper euro zone political integration.
Ayrault said earlier on Sunday that any steps towards European federalism would need to ensure that national parliaments provided oversight.
Hollande lacks the two-thirds majority he would need to make constitutional changes that would be required for example to give EU institutions more control over national budgets, a key concession demanded by Berlin in return for more fiscal support.
"Hollande will certainly feel emboldened to carry things through and negotiate at the European Council," said Christopher Bickerton, associate political science professor at Sciences Po.
"Momentum is building for him. Whether he can garner that to push forward his agenda in Europe is the most crucial question."
Additional reporting by Leigh Thomas, Geert De Clercq, Nicholas Vinocur and Gus Trompiz in Paris and Claude Canellas in La Rochelle; Editing by Paul Taylor