The far-right candidate explained she was moving away from the Front National party to concentrate on her presidential bid, with her move further distancing herself from former FN leader, her maverick father Jean-Marie.
Far-right presidential contender Marine Le Pen said Tuesday that people are revolting against the elite and predicted that could translate into a "very big surprise" when ballots are cast May 7 in France's final round to choose a new leader - and it will be her.
"I will feel freer, I will be above partisan considerations, it's an important act", Le Pen told France 2 television. "I am the candidate for the French presidency", she said.
Snap polls released late Sunday showed 39-year-old Macron winning the runoff easily by a margin of around 60-40 percent, meaning Le Pen needs to make up more than 10 points in the next two weeks.
President Hollande said the far right would threaten the break-up of Europe, "profoundly divide France" and "faced with such a risk, I will vote for Emmanuel Macron".
The next and decisive round of voting will be held on 7th May and it will be the first time in six decades that neither of France's main left-wing of right-wing parties has had a candidate in the second round.
It is the first time in the history of the modern French Republic that the presidency will be held by a member of a non-traditional party, highlighting a deep anti-establishment sentiment that ultimately could determine whether France remains a part of the European Union or follows an independent path like that of post-Brexit Britain and the United States under Donald Trump.
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"The 21 percent vote for Le Pen is also a result of German politicians' lecturing attitude towards others in Europe", he added.
One theory is that Le Pen's decision is largely cosmetic.
"Giving a platform to Marine Le Pen and the FN has enabled the worst racism and anti-semitism to grow again in France", said UAF joint secretary Sabby Dhalu.
This judgment of Mr Macron is still strongly felt among numerous Mr Sarkozy-faction on the right-wing of The Republicans though others, loosely represented by more moderate ex-prime minister Alain Juppe, have suggested they may choose to join in a majority of support for Mr Macron.
Hitting that angle in Rouvroy, Le Pen, after urging "all patriots" on Sunday to rally behind her, on Monday handed out leaflets in which she pledged to "eradicate Islamist terrorism" and expel "Islamist foreigners".
Le Pen appears to have a mountain to climb, however.
In the rest of French-speaking Switzerland Macron narrowly beat Fillion, with the two candidates taking 33 percent and 31 percent of the vote respectively.