Born on July 3, 1979 in La Celle-Saint-Cloud, in France's Yvelines department, Ludivine Sagnier used to play piano in her early years to please her father. Her mother was a retired secretary and her father was a professor of English at the Paris University, who came from a family of musicians and wanted his daughter to play a musical instrument.

However, she did not like music theory and finally ended up following her sister to the theatre, started to take classes in Sèvre and began to take some castings. She made debut in her first feature film at the early age of ten when she starred in the French comedy film Les maris, les femmes, les amants (The Husbands, the Wives, the Lovers - 1989), directed by Pascal Thomas and then in I Want to Go Home (1989), directed by Alain Resnais, followed by her small role of the little sister in Cyrano de Bergerac (1990), directed by Jean-Paul Rappeneau and starring Gérard Depardieu. In 1992, Ludivine Sagnier appeared as Anne-Sophie in the television series La Famille Fontaine and after that starred several television movies like Les enfants du siècle (Children of the Century 1999), and also played the role of Anna in the short film Animated Acid (1999), for which she won the best actress award in the Les Acteurs a L'Ecran film festival in Saint-Denis, France.

However, Ludivine Sagnier established her reputation as one of the brightest young stars in French and international cinema, when she appeared in the role of Anna in Water Drops on Burning Rocks (2000), directed by François Ozon, and two years later, she also appeared as Catherine, alongside the greatest French actresses like Catherine Deneuve, Emmanuelle Béart, Fanny Ardant and Virginie Ledoyen in his crime-musical film 8 Women (2002), for which she earned a Cesar Award nomination for the Most Promising Actress, the Best Actress Award from the European Film Academy Award, the Silver Bear Award at the 2002 Berlin International Film Festival, as well as the Romy Schneider Award that is given each year to a promising young French actress.

But her performance in François Ozon's thriller Swimming Pool (2003), in which she appeared as Julie, a reckless and sexually charged nymphet, whose life of one-night stands becomes entangled in a real-life murder and unsettled the creative process of Sarah Morton, a famous mystery author, established her as an international star. For her performance in the film Sagnier again earned a Cesar Award nomination for the Best Supporting Actress, and with her blonde hair and alluring curves, Sagnier became a favourite to play the sexy seductress.

Following the American success of Swimming Pool, Sagnier received several offers to play the sexy seductress, but she deliberately avoided the trend and appeared as Tinker Bell in PJ Hogan's fantasy Peter Pan (2003). In the same year, she also appeared in La Petite Lili (2003), directed by Claude Miller and won the Silver Hugo Award for Best Actress in Chicago International Film Festival.

After that, Sagnier played her first English language role in Toothache (2006), in which she played the role of Anna, the young French partner of an English writer, followed by La Californie (2006), in which she played the role of Helène, a young woman in love. For her performance in Un secret (2007), the French drama film relating to the holocaust, directed by Claude Miller, in which she played the tragic role of Hannah, she earned another Cesar Award nomination for the Best Supporting Actress. Apart from that, she also starred in the period biographical drama Molière (2007), the French musical film Les Chansons d'amour (Love Songs 2007), the black comedy A Girl Cut in Two (2007), directed by by Claude Chabrol, and the French biographical crime film Mesrine is a two-parts, Mesrine: Killer Instinct (2008) and Mesrine: Public Enemy Number One (2008).

After that, Ludivine Sagnier played the role of Lily, a really strong force of nature, in Pieds nus sur les limaces (Lily Sometimes 2010), and also portrayed the role of Isabelle Guérin, an intelligent and cunning young woman in search of love, in the crime drama, Crime d'amour (Love Crime 2010), the last movie directed by Alain Corneau, who died just twelve days after the release of the movie. The next year, she appeared as Sarrab, in the terrifying, well crafted Horror drama The Devil's Double (2011), and as Madeleine Jeune, in the French romantic drama film Beloved (2011), directed by Christophe Honoré and also starring Catherine Deneuve.

Subsequent films of Ludivine Sagnier include, among others, the French romantic comedy film Love Is in the Air (2013), the French comedy drama Tristesse Club (2014), the French-Belgian drama film Through the Air (2015), the comedy-drama film Rémi sans famille (Remi, Nobody's Boy 2018), and La Vérité (The Truth 2019), also starring Catherine Deneuve and Juliette Binoche.

In her personal life, Ludivine Sagnier met French actor Nicolas Duvauchelle in 2004 on the set of Uni adventure (Only the Nightv 2005), and they began an intense relationship, giving birth to a daughter in 2005. But their relationship lasted only for three years, and they decided to be separated in 2007. Nevertheless, Sagnier has been in a relationship with Kim Chapiron, the French film director and musician of Vietnamese descent, since 2008, with whom she gave birth to two daughters, one in 2009 and the second in 2014. However, known for her modesty, Ludivine Sagnier very rarely talks about her private life.