The niece of French far right leader Marine Le Pen, Marion Marechal, on Sunday officially joined forces with a rival campaign for the April 2022 elections in a blow to her aunt's bid.

Marechal, 32, who had already hinted at her move, addressed a major rally of far-right pundit Eric Zemmour who over the last months has upstaged Le Pen by becoming a major presence in the campaign.

President Emmanuel Macron, who last week finally made clear he was standing, is the overwhelming favourite to win a new term, with Russia's invasion of Ukraine seen as bolstering his position by keeping other candidates in the shade.

"I am certain that political transformation will take place and I believe again that victory is possible," Marion Marechal told the rally in the southern port city of Toulon.

She hit out at Macron, calling him a "president of division".

Her defection and willingness to cause a family rift is a welcome boost for Zemmour who has started to slip in the polls in recent weeks after enjoying an initial surge when he declared his candidacy.

Marion Marechal is seen by may observers to be a future leader of far-right nationalist camp
Marion Marechal is seen by may observers to be a future leader of far-right nationalist camp AFP / CLEMENT MAHOUDEAU

Marine Le Pen had in January said she was personally hurt by Marion Marechal's plan to defect, saying: "It's brutal, it's shocking, it's difficult for me."

Polls currently suggest Le Pen and Zemmour are the main contenders to make a run-off against Macron, with the traditional right-wing candidate Valerie Pecresse failing to ignite her campaign.

An Ipsos-Sopra-Steria poll published Saturday showed Macron on course to win 30.5 percent in the first round, a reading that is up sharply since the start of Russia's war against Ukraine.

Le Pen is on 14.5 percent and Eric Zemmour 13 percent. Pecresse was put on 11.5 percent, eclipsed by far-left candidate Jean-Luc Melenchon on 12 percent.

Marion Marechal is seen by many observers to be a future leader of far-right nationalist camp.

Elected as the youngest member of parliament in 2012 at the age of 22, Marechal stepped back from frontline politics five years later to spend more time with her daughter and open a political sciences school focused on nationalism.