After studying film at IDHEC, Mariana Otero developed a passion for documentary filmmaking. She directed several films for Arte, including Non Lieux and La loi du collège, which was the channel’s first documentary series.

Between 1995 and 2000, she lived in Portugal, where she directed Cette télévision est la vôtre, which explores the inner workings of the country’s largest commercial television network, SIC. By exposing the inner workings of the country’s largest commercial television network, this film sparked a huge controversy in Portugal.

She then returned to France and turned her attention to feature films with Histoire d’un secret.

This film, following an investigation into a family secret, reveals a political and social taboo and brings to light the work of her mother, a painter who died suddenly in 1968 as a result of a clandestine abortion. A major critical and commercial success, the film won awards at numerous international film festivals.

In 2010, she directed Entre nos mains, which tells the story of how female employees discover a new freedom as they attempt to transform their company into a cooperative. This film was nominated for a César Award for Best Documentary in 2011.

In 2013, she directed A ciel ouvert, a film that offers insight into the unique worldview of children facing psychological and social challenges. As a follow-up to the film, she co-wrote the book A ciel ouvert, entretiens with Marie Brémond.

In 2016–17, she directed L’Assemblée, a film shot during the Nuit debout protests, which shows how people in Place de la République in Paris attempted to reinvent democracy.

In 2019, she directed Histoire d’un regard about photojournalist Gilles Caron. A sort of second part of a diptych that it forms with Histoire d’un secret, this film brings a deceased artist back to life and into the present by examining and questioning his images. The film was selected for numerous international festivals and nominated for a César Award for Best Documentary in 2020.

In 2026, she completed her new film, D’un corps à l’autre, which chronicles a dance workshop with visually impaired and neurodivergent participants, where she collaborated with a sound designer who helps convey the sensation of touch and bodily movements. This joyful film - as sensory as it is political - celebrates difference and art as a special space for encounter and sharing.

In addition, she teaches at the Ateliers Varan, where she has been a member since 2000; at La Fémis; at the University of Jussieu; at Creadoc (University of Poitiers/Angoulême), where she headed the Master 2 program in Creative Documentary for six years (2006–2012); at ECAL (Lausanne); and elsewhere. She is a member of the SRF and of ACID, where she served as co-president from 2010 to 2012. She is a member of the Association des Amis du cinéma du réel, where she served as co-president from 2020 to 2022.

In 2011, she was named a Chevalier des Arts et des Lettres.

In 2025, she founded the association Aux avortées inconnues to erect a monument in Paris dedicated to women who died from clandestine abortions. She directed Lettres pour un avortement clandestin at the Maison de la Poésie and the Théâtre de la Concorde, featuring 17 actresses, including Anne Alvaro, India Hair, and Clotilde Hesme…