Born in the French Ardennes in 1983, Guillaume Massart works across creative documentary as a director, producer and editor. 

In 2010, he co-founded the production company TRIPTYQUE FILMS with two partners.

His first eleven films screened widely at festivals. THERE BE NO DRAGONS was selected for competition at Cinéma du réel in 2010. Two years later, he returned to the festival with HIJACKING THE BOX, co-directed with Julien Meunier.

Written at the Villa Medici in Rome, SAVAGE FLOWERS received the Art & Caméra Award at the Festival of Art History and was presented at Cinéma du réel in 2017. Centred on a collection of prison-made objects assembled by an unconventional anthropologist, this mid-length film opened a trilogy exploring the world of prisons.

His first feature, IN THE OPEN, was shot over the course of a year at Casabianda, on Corsica’s eastern plain. At this unusual detention centre, set within a vast agricultural estate, walls, bars and watchtowers have given way to trees, sky and sea. As the seasons pass, Massart observes the prisoners’ everyday gestures and records their voices as they gradually grow freer, exploring how imprisonment in the open air alters the experience of serving a sentence.

Before its French theatrical release in February 2019, the film travelled widely on the international festival circuit, screening at festivals including Visions du Réel, IDFA, IndieLisboa, Entrevues Belfort, the Millennium Documentary Film Festival in Brussels and Kasseler Dokfest. It received the Audience Award at the Rencontres du cinéma documentaire in Montreuil and the Île d’Or Award at the Festival international du film insulaire in Groix. In 2023, Neige Sinno devoted several pages of her best-selling book Triste Tigre to the film, which becomes a work she thinks both with and against in her reflections on incest.. 

His second feature film, DETENTION, brings this prison trilogy to a close by shifting its focus to what comes before prison: the training of those who will work inside it. Shot on the campus of France’s National School for Prison and Probation Services, the film follows trainee prison officers as they learn a profession—its gestures, its rules and its contradictions. Through this group of men and women of widely differing ages and backgrounds, all preparing to work in prisons, Massart observes how the institution shapes bodies and prepares each individual to exercise authority.

DETENTION began its international festival journey at ACID Cannes in 2026. The film is also notably showcased at the FEMA in La Rochelle, at Lussas, at Gindou, and further afield in South Korea at the DMZ Documentary Film Festival. Les Alchimistes will distribute it in French cinemas in the first quarter of 2027.