The veteran defender has signed for Jurgen Klopp's side in the wake of an injury crisis ahead of Saturday's meeting with Bayern Munich
The former Bayer Leverkusen defender, 34, joins the Champions League hopefuls on a contract until the end of the season.
The deal follows the news that Mats Hummels will be out of action until 2014 after he suffered a broken foot during Germany’s 1-0 friendly victory over England.
With Neven Subotic also sidelined, Jurgen Klopp’s side had faced something of a central defensive crisis ahead of Saturday night’s Bundesliga clash against league leaders Bayern Munich at Signal Iduna Park.
Nevertheless, they remain weakened throughout their back four as Marcel Schmelzer picked up a calf problem while on international duty, too, and joined Hummels and midfielder Ilkay Gundogan on the treatment table.
While Friedrich is eligible to turn out in the Bundesliga, he will not be able to feature in BVB’s remaining Champions League group stage encounters against Napoli and Olympique de Marseille.