The feisty 48-year-old, who lost by a 20-point margin to Emmanuel Macron in May's presidential run-off, won handily in her northern fiefdom of Henin-Beaumont, a depressed former mining town, with 58 percent of the vote, she announced.
But her anti-EU, anti-immigration FN failed to capitalise on the populist wave that helped propel Donald Trump to the US presidency and spurred Britain's vote to leave the European Union.
Le Pen said her party had won "at least" six seats in the 577-seat National Assembly, dashing her one-time hopes of emerging as the main opposition to Macron's centrist Republic on the Move (REM) party.
Le Pen said nevertheless that the FN, "against a bloc that represents the interests of the oligarchy, are the only force of resistance."
REM and its centrist ally MoDem were projected to have won a massive majority of between 355 and 403 seats.
Le Pen, like radical left leader Jean-Luc Melenchon, said record low turnout projected at around 44 percent cast doubt on REM's legitimacy.
In late April, after Le Pen qualified to face off with Macron, Bruno Jeanbart of the OpinionWay polling institute said the FN could hope to win between 20 and 50 seats.
But by falling short of 15 seats in the end, the FN will be too small to form a parliamentary group which would have given it a role in setting the parliamentary agenda as well as influential committee positions.
In the presidential election, Le Pen won more than 50 percent of votes in her head-to-head with Macron in 45 voting districts and drew a total of 10.7 million votes, a historic high for the far-right party.
The FN has two lawmakers in the outgoing parliament, one of whom will not return.
Le Pen's 27-year-old niece Marion Marechal-Le Pen, a darling of the FN and the face of its traditional Catholic base, shocked grassroots supporters by announcing her decision not to seek re-election.
Marechal-Le Pen announced the decision just two days after her aunt lost to Macron.
The other incumbent, Gillard Collard, won by just 123 votes over a former bullfighter, Marie Sara, one of dozens of new MPs in the REM party with no prior political experience.
Senior FN figure Florian Philippot, the architect of the FN's policies to scrap the euro common currency, lost in the former industrial area of Moselle in eastern France.
Le Pen was seen as a shoo-in for the Henin-Beaumont seat after scoring 46 percent in the first round a week ago against 11 rivals, and she defeated a political novice from Macron's party, Anne Roquet.
Le Pen fought for the same seat in 2012, losing by 118 votes to the Socialist Philippe Kemel, who was eliminated this year in the first round of the parliamentary election last Sunday.
Le Pen complained last weekend that the record low first-round turnout raised questions over France's two-round first-past-the-post system that favours larger parties.
On Sunday she said it was "scandalous" that the FN could not have a group in parliament.
In 1986, under a proportional representation system, the FN, then led by her father Jean-Marie Le Pen, won 35 seats.
The FN leader will now have to abandon her seat in the European Parliament, where her party is under several investigations in alleged funding scandals.
Le Pen and the FN were seen as likely to benefit this year from a confluence of factors including the 2015 migrant crisis and the string of jihadist attacks that have hit France.
The party has a particular populist appeal in France's northern rustbelt, which is dotted with shutdown factories and mines.
Le Pen was roundly criticised for a poor performance in a brutal TV debate with Macron days before the presidential runoff that probably cost her votes.
Le Pen has spent the past six years since taking charge of the FN trying to expunge the xenophobic, anti-Semitic ethos engendered by her father, who co-founded the party in 1972.
Under Marine Le Pen, the FN has consistently improved its electoral scores, notching up records in past regional, European Parliament and presidential elections.