Born in 1963, Mariana Otero studied cinema at IDHEC (La Femis film school) before turning her attention fully to documentary filmmaking. She has made several films for Arte, including ==Non Lieux== and ==La loi du college==, the channel's first documentary series. Between 1995 and 2000, she lived in Portugal, where she made ==Cette télévision est la vôtre==. By revealing the workings of the country's largest commercial television channel (SIC), this film created a huge controversy in Portugal. She then returned to France and turned to broader cinema with ==Histoire d'un secret==. At the end of an investigation into a family secret, this film reveals a political and social taboo and revives the work of her mother, a painter who died suddenly in 1968. It won many awards at various international film festivals. In 2010, she directed ==Entre nos mains==, which tells the story of how a group of employees discover a new freedom by trying to transform their company into a cooperative. The film was nominated for a César for Best Documentary in 2011. In 2013, she directed ==A ciel ouvert==, a film that provides an insight into the unique vision of the world held by children who are psychologically and socially disadvantaged. As an extension of the film, she and Marie Brémond wrote the book ==A ciel ouvert, entretiens==. In 2016/17, she directed ==L'Assemblée==, a film shot during Nuit debout, which shows how people on the Place de la République in Paris were trying to reinvent democracy. In 2019, she directed ==Histoire d'un regard== about photojournalist Gilles Caron. This film forms a sort of diptych mirroring Histoire d'un secret. This film gives modern life and presence to an artist who has disappeared, by taking an interest in and questioning his images. She has taught at the Ateliers Varan, of which she has been a member since 2000, at the Femis, at Sorbonne Paris III University, at Creadoc (University of Poitiers/Angoulême), where she was head of the Master 2 in Creative Documentary for six years (2006-2012), and at the ECAL (Lausanne). She is a member of ACID, of which she was co-president from 2010 to 2012.