Thorsten Merten was born in Ruhla near Eisenach in 1963. He originally wanted to become a journalist, but his plan was denied by GDR authorities, because he gave a satirical performance at a local cabaret. Merten then decided to study acting at the Berlin Hochschule für Schauspielkunst "Ernst Busch" and graduated with a diploma in 1990. After his graduation, he got engagements at various stages throughout Europe, including Ruhrfestspiele Recklinghausen and the Théâtre Vidy Lausanne. He became an ensemble member at the Staatstheater Schwerin from 1992 to 1994 (and from 1999 to 2003).

Merten made his film debut in Andreas Dresen's award-winning film "Stilles Land" (1992), a drama about the German reunification. A minor part in Joseph Orr's comedy "Oben-Unten" (1994) was his last appearance in a film until 2001. He focused on his stage career instead and received the Conrad-Ekhof-Award in 1999.

He made a successful comeback on the big screen with the award-winning film "Halbe Treppe" ("Grill Point", 2001/02) for which he received an award for "Best Actor in a Leading Role" at the Festival du Cinéma Européen in Paris. In the following years, Merten had minor parts in several films, including Dito Tsintsadze's "Schussangst" ("Gun-Shy", 2003), Eoin Moore's "Im Schwitzkasten" ("No Sweat", 2005), Aelrun Goette's "Unter dem Eis" ("Under the Ice", 2005), Oskar Roehler's "Elementarteilchen" ("The Elementary Particles", 2006) and Maximilian Erlenwein's "Schwerkraft" ("Gravity", 2009). In "Vier Fenster" ("Four Windows", 2006, director: Christian Moris Müller), Merten had a starring role as an unemployed father.

In 2004, he got engagements at the Maxim-Gorki-Theatre in Berlin where he mostly worked with Volker Hesse. Since 2008, Merten is an ensemble member at the Volksbühne Berlin where he appeared in Dimiter Gotscheff's production of "Iwanow" (2008) and Aischylos's "Prometheus" (2009), and also in "Hunde" ("Dogs", 2008) und "Nord" ("North", 2009) which are based on novels by Louis-Ferdinand Céline.

Apart from working for film and theatre productions, Merten appeared in popular German crime series, including the "Tatort" episode "Die fette Hoppe" where he played alongside Christian Ulmen and Nora Tschirner. He is also well-known for his role as chief inspector Fichte in the "Spreewald-Krimi" installments.

In his latest collaboration with Andreas Dresen, the highly acclaimed drama "Halt auf freier Strecke" ("Stopped on track", 2010/12), Merten gives a human form to the protagonist's cerebral tumor. The same year, he also appeared in the anthology film "Ruhm" ("Glory: A Tale of Mistaken Identities") directed by Isabel Kleefeld and starring Gabriela Maria Schmeide, Senta Berger, Heino Ferch and Julia Koschitz. In Nico Sommer's tragedy "Silvi" ("Silvi - Maybe Love"), which premiered at the Berlinale 2013, Merten plays the ex-husband of the protagonist (Lina Wendel).

In 2014, he returned to the stage at Staatstheater Schwerin with an engagement in "Sonnenallee – Das Musical", based on the film by Thomas Brussig, Detlev Buck and Leander Haußmann. Merten also played in Michael Baumann's "Willkommen bei Habib" ("Habib Rhapsody"), which premiered at the Hofer Filmtage in 2013.

For Aron Lehmann's "Kohlhaas oder Die Verhältnismäßigkeit der Mittel" ("Kohlhaas Or The Proportionality Of Means") he was awarded the German Actors' Prize with the ensemble in 2014. This was followed by roles in highly acclaimed works such as "Wir sind jung. Wir sind stark" ("We Are Young. We Are Strong." 2014), "Bornholmer Straße" (TV, 2014) and "Fremdkörper" (TV, 2015), in which he played the recipient of an illegally donated kidney. He also had supporting roles in the comedies "Alki, Alki" ("Alky, Alky", 2015), "Die letzte Sau" ("The Last Pig", 2016) and "Petting statt Pershing" ("Good Girl Gone Bad", 2018), as well as in the lavish hit series "Babylon Berlin" (2017-2020).  

David Nawrath cast Merten in a central supporting role in his multi-award-winning drama "Atlas" ("The Mover", 2017), and in the TV series special "Der vierte Mann" (2019) of the "SOKO Wien"/"SOKO Leipzig" series, Merten played the lead role of a janitor who wants to avenge the death of his former fiancée. In Sergei Loznitsa's war drama "Donbass" (2018), he had a small role as a German journalist. He worked again with Andreas Dresen in the acclaimed biopic "Gundermann" (2018), which won six German Film Awards.  

At the Berlinale 2020, Johannes Naber's "Curveball" premiered, a satirical political thriller about true events in the run-up to the U.S. invasion of Iraq, in which Merten portrayed a jovial BND department head. For his outstanding performance, he received the Lola in the Best Supporting Male category at the 2021 German Film Awards. 

Mertens had further big screen roles as the professional father of a suicidal teenager in "Nothing More Perfect" (2020) and as a prison guard in the neighbourhood story "In Berlin wächst kein Orangenbaum" (2020). On television, he continued to play Chief Inspector Kurt Stich in the Weimar "Tatort" episodes and Chief Inspector Fichte in the "Spreewaldkrimi." 

In 2022, two films starring Mertens were released: in Sönke Wortmann's teacher comedy "Eingeschlossene Gesellschaft" ("Locked-In Society"), he had a leading role as an angry father, and in the children's film "Alfons Zitterbacke - Endlich Klassenfahrt!" he played a teacher.