Le Pen secured 34 percent of the votes in the presidential runoff vote versus 66 percent for the pro-EU Macron.
"Yes, I will be a candidate", she said on French TV channel TF1, confirming she will run in the northern town of Henin-Baumont.
"I can not imagine not leading my troops in this fundamental battle", she said.
Centrist Macron gave ministerial jobs to conservatives, socialists and newcomers to politics on Wednesday, appointing an unprecedented all-stripes cabinet to bridge traditional divides and broaden his support.More news: Rosenstein knew Comey would be fired before writing memo, Dem senators say
Marine Le Pen's 33.9 per cent showing against Macron weakened her standing in the party, even though she racked up an historic 10.6 million votes.
Le Pen's heavy electoral defeat has prompted soul-searching within the far-right FN with some blaming her commitment to quitting the euro zone for the outcome.
Ms Le Pen would have been forced to "cohabit" with a government and prime minister from a different party, which she could have changed only if she won a parliamentary majority - an unlikely prospect.
"We are going to have to take this into account, discuss and reflect".