Fehling was born in Berlin, Germany on 29 March 1981. He studied acting at the Ernst Busch Academy of Dramatic Arts from 2003 until 2007.
Fehling received the Förderpreis Deutscher Film award in the category of drama for his portrayal of Sven Lehnert in the 2006 film, And Along Come Tourists. He had previously won the OE Hasse Prize from the Akademie der Künste, Berlin for his role as Prince in the theater production of Schneewittchen (Snow White).
Fehling is best known to English-speaking audiences for his role as German Master Sgt. Wilhelm in Quentin Tarantino's World War II 2009 film Inglourious Basterds. Fehling is incorrectly referred to as a Staff Sgt by the English captions. Fehling also dubs his performance in the German version of the film.