Le Pen, 48, spoke in Paris at a joint press conference with Dupont-Aignan, 56, leader of the Debout la France (Arise France) movement, the sixth most-voted political formation during the April 23 presidential first round, with 1.7 million votes.
In a speech before the gilded statue in Paris of Joan of Arc, his heroine, Jean-Marie Le Pen urged French voters to back his daughter in Sunday's runoff.
French centrist presidential candidate Emmanuel Macron, 2nd left, stands next to Said Bouarram, left, son of Brahim Bouarram, as he pays hommage to Brahim Bouarram, a Moroccan who drowned in 1995 when right-wing extremists threw him from a bridge after a National Front rally, during a ceremony on the banks of the Seine River in Paris, France, Monday, May 1, 2017.
Speaking after attending an European Union summit on Saturday, outgoing French President Francois Hollande warned voters that abstaining on May 7 could help Le Pen score high enough to encourage her to run again if she isn't elected this time.
Yet the gesture can not undo decades of anti-Semitism that still poisons her party.
Jean-Marie Le Pen was expelled from the party's management in 2015 after he said World War Two Nazi gas chambers were a "detail" of history, but he remains an honorary president of the National Front. Mr Macron called, in the Journal du Dimanche newspaper, for a new "arch" reaching across left and right to rebuild French politics.
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His wife Mireille said, "I have always voted conservative, and it will be hard to betray my political convictions, but I have no other choice".
"Ms Le Pen adopts an approach that builds on the fear from political Islam and on the refusal of Muslim integration in the European Community".
"She wants to demolish the euro", Pau Mayor Francois Bayrou said on RTL radio.
Marine Le Pen, Macron's extreme-right rival in the run-off of the presidential election, due to take place on May 7, has contested this responsibility. There was no national atonement, and families across France have troubling stories of collaboration that have been hidden from their children and grandchildren.
Despite Chirac's gesture, many French prefer to see the Vichy regime that governed wartime France as a historical anomaly. The bloc has already been rattled by Britain's exit, or Brexit. "This contract for a governmental alliance will be key to get beyond the divisions and the doubts that are giving the "system" and Emmanuel Macron the weapons they need to survive, thus harming the national interest", the two signatories stated.
Macron, on a campaign trip in central France where he called politicians who do not back him "morally weak", said on Saturday the alliance between Dupont-Aignan and Le Pen clarified the choice on offer to voters.
"What I'm saying, and what really surprised me, in the work of a genuine negationist or revisionist.is the well-worked, rigorous nature of the argument put forward", Mr Jalkh was quoted as saying. And if you map the votes that Le Pen and Macron geographically, Le Pen will emerge victorious with eight of the 18 regions while Macron trails behind with only six regions.