Her grandfather, Jean-Marie Le Pen, founded the Front National party on 5 October 1972. Her aunt Marine Le Pen has been FN President since 16 January 2011, with Jean-Marie Le Pen first becoming honorary chairman and later excluded in August 2015. Her mother Yann Le Pen, Jean-Marie Le Pen's second daughter, does not carry out any official duties within the FN. Her father Samuel Maréchal had been the leader of the Front National Youth movement (FNJ) for seven years (1992–1999). She featured with her grandfather in a campaign poster at the age of two.

She was born on 10 December 1989 in Saint-Germain-en-Laye, Yvelines, Île-de-France.

She is the only member of the National Front since 1997 to have served in the National Assembly. A member of the FN from 1972 to 2005 and an MP for Vaucluse under the eighth legislature (1986–1988), Jacques Bompard, was also elected as an MP for Vaucluse's 4th constituency. Gilbert Collard, a member of the Rassemblement bleu Marine, a political association that supports Marine Le Pen, was also elected as an MP.

She was a candidate in seventh position on the FN list in Saint-Cloud, Hauts-de-Seine, in the 2008 municipal elections. She was not elected, for the FN list only got 6.29% with one municipal councillor elected from the first round.

In the 2010 regional elections, she figured in second position on the FN departmental list in the Yvelines, Île-de-France. Marie-Christine Arnautu's FN list, which polled 9.29% in the whole of Île-de-France in the first round, could not take part in the run-off, given that a list must cross a threshold of 10% of the valid votes at a regional level. Because of the process of elimination, she was not elected in the Île-de-France's regional council.

One of the six youngest members of the new Assembly, Maréchal-Le Pen served on 26 June 2012 as a secretary during the opening of the fourteenth legislature presided over by the most senior member François Scellier.

Maréchal-Le Pen was a Non-Attached member of the National Assembly. Her seat (number 67) was located between the ones of Gilbert Collard (number 66, on her right) and Jacques Bompard (number 68, on her left). The National Assembly has included eight unregistered MPs since 30 August 2013.

In the first round on 23 March 2014, the FN list led by Gérard Gérent, which was defeated by the one of the UMP incumbent mayor Thierry Lagneau, came second with 33.80% (2,861 votes) with the election of five municipal councillors and two community councillors. Consequently, she was not elected as a municipal councillor at Sorgues.

In April 2015, because of his intense anti-FN campaign in the departmental elections, Maréchal-Le Pen criticized the "cretinous contempt" ("mépris crétin") of Socialist Prime Minister Manuel Valls in parliament. Valls responded with a trembling hand and an apparent fury. After it had become a viral video, Maréchal-Le Pen explained it was a reference to Michel Onfray, who has also called Valls a "crétin" when the Prime Minister has accused him of "losing his landmarks".

After retiring from politics in 2017, Marion Marechal-Le Pen enrolled in a Master of Business Administration (MBA) at EMLYON Business School.

Maréchal-Le Pen believes that Muslims can only be French if they follow the Christianity-shaped culture, saying that "In our country, we don’t wear djellaba clothing, we don’t wear a veil and we don’t impose cathedral-sized mosques".