The Front National's nationalist Marine Le Pen returned from summer holidays "with a great determination and a burning sense of duty not for me but for you, not alone, but with you", she said on Saturday.
Speaking to a crowd of about 500 in the northeastern town of Brachay, a Front National stronghold, the populist leader said: "Our political family is the only one capable of embodying" a force that could counter the new centrist movement of President Emmanuel Macron.
Le Pen garnered 34 percent of the vote against 66 percent for Macron in the May presidential runoff.
In June, the Eurosceptic, anti-immigration FN went on to win eight seats in the 577-seat parliament.
While the result was a historic high for the FN, many within the party were deeply disappointed, claiming Le Pen had run a poor campaign.
The party split over its key policy of wanting to scrap the euro, seen as too risky by many voters, particularly from the older generation.
The radical left Unbowed France party of Jean-Luc Mélenchon, with 17 seats in parliament, touts itself as the country's leading opposition force.
But on Saturday, Le Pen, 49, said: "We are the exact antithesis of Macronism."
She lambasted the president for what she called a "policy of perpetual precariousness", in a reference to his reforms to the labour code that will make it easier for employers to hire and fire staff.
"Macronism is the triumph of the dominant class whose only moral veneer is human rights and whose only values and purpose is money," she said.
Le Pen called on all French people to join in a consultation on the party's future.
A congress, expected for early 2018, would choose a new name for the National Front, she confirmed.
"The great enterprise of re-founding the national movement to which I invite you... but also all French people, is inspired only by duty: the duty to take action and to win so that France can remain France for its children and for the world," Le Pen said.
"The new organization will bear a new name which we can discuss during our exchanges and which will be chosen by you," she promised supporters in the eastern French village of Brachay.
The National Front, founded by Le Pen's father Jean-Marie Le Pen, has been at odds about its political direction since the election.
Le Pen attacked Mélenchon's hard-left La France Insoumise as "Islamo-Trotskyists" and accused both him and Macron of supporting mass immigration and the "infiltration of terrorists into the heart of our societies."
"I say and will repeat to Mr Macron: We will not let ourselves be pushed around," she said.
Le Pen's speech comes as President Macron's most daring undertaking to date is underway; reforming France's nearly sacrosanct labor laws. Macron's reforms trim union powers, add a voice for small businesses and create easier ways to hire and fire workers.
The high-stakes move comes just as the new 39-year-old president's popularity is sinking. But plans to make the labor market more flexible were at the heart of his election campaign.
Opponents have feared changes will weaken France's hard-won worker protections that have become globally synonymous with the envied French lifestyle. Left-wing opponents fear the changes hand too much power to profit-focused bosses.