After earning a Baccalauréat at the Lycée Condorcet of Belfort, he enrolled first in Sports and then Computer Science programs. After two subsequent years of an unmotivated boredom with the subjects in Strasbourg and Marseille, Rahim decided to pursue his passion and began to study film at the Paul Valéry University of Montpellier. His life as a film student was chronicled in a documentary by Cyril Mennegun titled "Tahar, student", aired on French TV channel France 5 in 2006.
Following this, Rahim moved to Paris in 2005 and studied drama at the Laboratoire de l'Acteur under Hélène Zidi-Chéruy while working in a factory during the week, and in a night club on weekends to make ends meet.
In mid-2006, after signing with an agent, Rahim won a part in the hit Canal+ television series La Commune written by Abdel Raouf Dafri. Dafri penned the first draft of the script to A Prophet. Rahim then met Audiard when the two coincidentally shared a cab while the two were leaving a set. Tahar introduced himself saying that "I knew it was Audiard and I said I was a fan but I think I was a bit silly" and was afterward very surprised that Audiard remembered him enough to contact him about A Prophet. After a two-line appearance in 2008 horror movie Inside starring Béatrice Dalle, he went through a gruelling three months of auditioning. After eight callbacks, he landed his breakthrough role.
2007 - 2008: Libres sont les papillons in the role of the blind character Benjamin. The play was written by Leonard Gershe, directed by Hélène Zidi-Chéruy and staged at the Côté Court Theater, 11th arrondissement of Paris.