Graduated from the Conservatoire of Lyon in guitar and counterpoint, he continued his studies at the CNSMD (Conservatoire National Supérieur de Musique et de Danse) where he obtained a Licence of Composition and a Diploma in Orchestration, followed in 2015 by a Master of Composition, option Music For Image, in the Gilles Alonzo's class. Throughout his studies, in parallel with his creations for concert and dance, Valentin multiplied his experiences in a number of short films, including L'Infini directed by a certain Lukas Dhont. This highly acclaimed film will be rewarded at many festivals and will seal an artistic and friendly bond between the young composer and Girl's future director. In 2012, Valentin Hadjadj received the Award For Best Young European Composer at the World Soundtrack Awards of the Ghent Festival (Belgium). In 2015, he signed his first music for a feature film April and the Extraordinary World, a superb animated film directed by Franck Ekinci and Christian Desmares after the work of Jacques Tardi.

Valentin reveals the extent of his talent through his mastery of classical writing and programming tools. The film will win the Cristal for best feature film at the Annecy International Animation Film Festival and the Prize for the Best Original Music at the Monstra Festival in Lisbon. In addition, he is nominated for the France Musique - SACEM Prize and wins the Young Talent Prize awarded by UCMF. 2017 is another pivotal year for Valentin Hadjadj: He meets Lukas Dhont again for the splendid film Girl, which will win dozens of international prizes, including the Caméra d'Or and the prize for Best Actor (Un Certain Regard) at the 2018 Cannes Film Festival. The film is amazing, Valentin's music is remarkable and noticed.

In September 2019, the composer received the Ensor (Flamish equivalent of the César) for the best original music. While Valentin Hadjadj has since been the object of all attention, he has always been involved on the short side by multiplying experiences and encounters, a dynamic that he wishes to apply to animation, series and "classic" feature films, while remaining attentive to tomorrow's creation. Among his most recent scores are Peter Mackie Burns' British film Rialto, produced by Le Bureau, and Fabienne Berthaud's Un Monde Plus Grand, produced by Haut & Court, two films selected for the Venice 2019 Mostra.

He is also responsible for the original music of Claus Drexel's film Sous les Étoiles de Paris produced by Arches Films and Maneki Films, not to mention the Roger animation series (78 episodes of 7 minutes each) produced by Je Suis Bien Content for France Télévision. In 2022, he scored Lukas Dhont's 2nd feature Close, which won the Grand Prix at the Cannes Film Festival, among many awards. In 2023, Valentin composed the score for Noé Debré's 1st film Le Dernier des Juifs, followed by the score for Tessa Blake's New York film Boundary Waters.