Josef Mattes was born on 9th of October 1989 to actress Eva Mattes and artist Wolfgang Georgsdorf. His first appearance on TV was in "Der Schächter" (2003), an episode of the German crime series "Tatort" in which his mother played the detective chief superintendent. In the TV thriller "Franz" (2004), he again starred alongside his mother.

Mattes became known to a wider (young) audience for playing Louis von Eden in the crime series (2005-2007) on the German youth channel KIKA. He was the main character’s son in Alain Gsponer’s award-winning tragic comedy "Das wahre Leben" ("Life Actually", 2006, TV) and his role as the pubescent son of an estranged couple in Berlin in "Die Helden aus der Nachbarschaft" ("Heroes from the Neighbourhood", 2008) earned him a nomination for the New Faces Award. He played one of the main characters in the TV drama "Empathie" (2009) about three teenagers in Berlin from different social classes whose paths cross with disastrous consequences. Mattes could then be seen in smaller roles in the teenager comedy "Groupies bleiben nicht zum Frühstück" ("Single by Contract", 2010) and in the satire "Neue Vahr Süd" (2010, TV) as well as a year later in guest roles in two TV crime series, "SOKO Leipzig" and "Stubbe – von Fall zu Fall".

He starred in one of the lead roles of the much praised coming-of-age film "Silent Youth" (2012) and four years later in the experimental feature film "Continuity", which celebrated its premiere at the Berlinale in the Forum Expanded section. In 2018, Philip Gröning’s drama "Mein Bruder heißt Robert und ist ein Idiot" ("My Brother's Name is Robert and He is an Idiot") premiered in the Berlinale competition with Josef Mattes playing the main character Robert who has a complicated relationship with his twin sister (Julia Zange). The shooting for this film had already been completed in 2013.