Lawmakers voted by a “big majority” to deprive Le Pen of her immunity in the case, launched by French prosecutors in 2015, acting parliament speaker Dimitrios Papadimoulis said.
French prosecutors opened an investigation in December 2015 into the graphic series of tweets by National Front leader Le Pen, which included a photo of the decapitated body of US reporter James Foley.
On Tuesday the legal committee of the European Parliament backed a request by the prosecutors for Le Pen's immunity as a member of the EU's only elected assembly to be lifted, officials told AFP.
“This only shows French citizens what the EU is, what the European Parliament is and that it's all part of the system that wants to stop the French people's candidate that I am,” the anti-EU candidate said in response to the move.
Le Pen has so far refused to attend a police interview over the investigation by police in the Paris suburb of Nanterre, citing her status as an MEP.
But her head of cabinet has been placed under formal investigation for “the dissemination of violent images”.
The eventual lifting of her immunity would concern only the tweets and not the ongoing probe into allegations that Le Pen misused public funds by hiring a fake parliamentary aide.
The images were tweeted with the caption “This is Daesh” (an Arabic acronym for the Islamic State group) and showed Foley's bloodied body with his decapitated head on his torso, a man on fire in a cage, and a victim being driven over by a tank.
Foley, a freelance journalist, was captured in Syria in 2012 and beheaded in August 2014.
Le Pen, who has over 830,000 Twitter followers, addressed the tweets to BFM TV journalist Jean-Jacques Bourdin, whom she accused of likening her party to the jihadist group.
Foley's bereaved parents John and Diane said they wanted the images removed immediately, accusing Le Pen in a statement of using the “shamefully uncensored” image to her own political ends.
A probe was also opened against Gilbert Collard, a National Front lawmaker in France, who had tweeted a similar violent image on the same day and for the same reason.
But last Wednesday the French national assembly refused to consider a request to lift his immunity after deciding it was not “sufficiently specific”.