The anti-immigration party stunned the French political establishment last week when it claimed the largest share of the national vote in the first round of regional elections
It also led in six of France's 13 regions, prompting the governing Socialist Party to yank candidates who were trailing in key regions to avoid splitting the anti-National Front vote.
National Front leader Marine Le Pen, who had appeared to be on the cusp of winning the northern region of Nord-Pas-de-Calais-Picardie, lost out to center-right candidate Xavier Bertrand, who won 56% of the vote to her 44%.
Her niece, Marion Marechal-Le Pen, thought to be one of the party's best hopes, was beaten by a similar margin in the southern Provence-Alpes-Cote d'Azur.
While the results eased immediate fears in the mainstream parties, Socialist Prime Minister Manuel Valls stressed there wasn't any room for complacency.
"Tonight, no sigh of relief, no sign of triumphalism," he said. "The danger of the far-right is still around."
Eyes on 2017
Although the National Front failed to win any regions, its share of the vote across the country remained above 27%, indicating support from a significant proportion of the electorate.
Going into the regional elections, the party had capitalized on security concerns and anti-immigration sentiment in the wake of last month's deadly terrorist attacks in Paris
Le Pen seemed unfazed by the second-round results, vowing that her party's fight for France was just beginning and that she'd be back on the ballot in the 2017 presidential elections.
"Nothing will be able to stop us," she said in a speech after the vote.
Le Pen said the party's increased share of the vote, roughly triple the percentage it secured five years ago, would make it "the main opposition force in most of the regional councils of France."
Her father and predecessor Jean-Marie Le Pen, who led the National Front from its foundation in 1972 until 2011, tweeted that the party had "lost a battle but will win the war."
Le Pen has 'huge springboard' for presidential vote
The party's performance gives Marine Le Pen "a huge springboard" for the 2017 election, said CNN contributor Stefan de Vries.
"The French National Front is now really part of the French political system, which was, until recently, a bipartisan system just like in the United States," de Vries said.
France's two mainstream parties won control of most of the country's mainland regions.
Former President Nicolas Sarkozy's center-right party, Les Republicains, won seven; President Francois Hollande's Socialist Party won five.
Voting in shadow of Paris attacks
The regional elections were the first to be held in France under a state of emergency imposed in response to last month's deadly attacks by Islamic extremists in Paris that left 130 people dead.
ISIS claimed responsibility for the attacks. In response, Hollande vowed to destroy the terror group and set about strengthening international efforts to wage a military campaign targeting ISIS territory in Syria and Iraq.
The rise of attacks by Islamist terrorists, combined with the migrant crisis that has seen hundreds of thousands of mostly Muslim immigrants cross into Europe, has fed support for the National Front's anti-immigration policies.
Le Pen told CNN's Hala Gorani in the wake of the Paris atrocities that Europe's acceptance of migrants on such a scale was "crazy."
"I had also warned ... the authorities very clearly that there will be in these immigrants terrorists, who will infiltrate ... and that's exactly what has happened," she said.
The National Front came in third after the second round of voting in the previous regional elections in 2010, and third in the most recent legislative elections in 2012
, earning the party two seats in the National Assembly.
In May last year, the party had unprecedented success in France's European elections
, winning 25.41% of the vote -- enough for 23 seats in the European Parliament.