Katrin Schlösser was born in Leipzig (then GDR) on May 23, 1965. Through her mother, who worked at the Berliner Ensemble theatre, she came into contact with the world of performing arts at an early age (opera director Ruth Berghaus was a close family friend). Schlösser trained as a mechanical engineering technician until 1982, followed by a traineeship at the German television station Deutscher Fernsehfunk (DFF). In 1984, she began studying film and television business at the Hochschule für Film und Fernsehen 'Konrad Wolf' in Potsdam-Babelsberg. She graduated in 1988 with a thesis on documentary filmmaker Volker Koepp. After her studies, Schlösser first worked as a production manager at DFF (1988-89), then as a production manager at DEFA's studio for documentaries (1990).    

After an internship with producer Renée Gundelach, she founded ö-Filmproduktion in 1990 together with Frank Löprich. One of their first productions caused a stir: "Stau - Jetzt geht's los" (1992), Thomas Heise's soberly observed portrait of young right-wing extremists in Halle. At the German Film Critics' Award, "Stau" was named Best Documentary. Yilmaz Arslan's feature debut "Langer Gang" (1992), about a group of young people searching for closeness and love in a rehabilitation center for handicapped youths, also received much attention due to its unusual subject matter.  

In the following years ö-Film produced documentaries such as Volker Koepp's "Die Wismut" (1993), Andreas Voigt's "Otspreußenland" (1996) and Thomas Heise's "Barluschke" (1997), as well as feature films such as Bernd Michael Lade's "Rache" (1996) and Karsten Laske's "Edgar" (1997), for which Lösser and Löprich won the Producer's Prize at the Saarbrücken Max Ophüls Festival. A very big success was "Sonnenallee" ("Sun Alley", 1999), co-produced by ö-Film: Leander Haußmann's humorous East Berlin milieu study drew over 2.6 million moviegoers to theaters and won the German Film Award in silver.  

In the noughties, ö-Film continued to mainly produce idiosyncratic auteur films outside the mainstream, both in the field of documentary and fiction film. As the German newspaper taz wrote in a portrait of Schlösser in 2011, she sees herself not only as a bureaucratic producer, but rather "as a consultant and enabler." Thus she produced Thomas Heise's "Neustadt Stau - Stand der Dinge" (2000) and "Kinder. Wie die Zeit vergeht." ("Children. As Time Flies", 2008), award-winning sequels to the documentary "Stau". Other significant productions/co-productions included Stefan Krohmer's family drama "Sommer '04 an der Schlei" ("Summer '04", 2006), Elke Hauck's impressive steelworker documentary "Karger" (2007), Lars Kraume's dystopian "Die kommenden Tage" ("The Coming Days", 2010) and Christian Schwochow's multiple award-winning GDR escape story "Westen" ("West", 2013), to name just a few.  

Schlösser has a long-standing collaboration with Ulrich Köhler: ö-Film produced his films "Montag kommen die Fenster" ("Windows on Monday", 2006) and "Schlafkrankheit" ("Sleeping Sickness", 2011), and co-produced "In My Room" (2018) and "Das freiwillige Jahr" ("A Voluntary Year", 2019; directed with Henner Winckler). All four films screened at major festivals (e.g. Berlin, Cannes, Locarno) and some won awards.  

In addition to her work as a producer, Katrin Schlösser has been a professor for creative film and television production at the Academy of Media Arts Cologne (KHM) since 2007. She has worked on the FFA's awards committee, served on the selection committee of the Berlinale competition, and was a member of the advisory board of the Goethe-Institut, among others. In 2019, she was elected Chair of the Board of Trustees of the DEFA Foundation (succeeding Andreas Dresen). She is married to the Austrian writer Lukas Lessing and lives in southern Burgenland and Berlin.   

Schlösser presented her directorial debut at the Diagonale in Graz in March 2019: For the long-term documentary "Szenen meine Ehe" ("Scenes from my Marriage"), which she began in 2015, she used her cell phone to capture moments of her married life, from romantic situations to serious crisis conversations. Due to the Corona pandemic, the film was not released theatrically as planned, but as VoD in April 2021.