He starred in the series Freunde wie wir as Thomas Reuter in 1997. Martinek’s best known role came as Max Zander/Der Clown in the German TV series Der Clown from 1998 to 2001. From 2006 to 2007 he starred in the television series Die Spezialisten: Kripo Rhein-Main. From 2006 to 2013 Martinek starred as Dr. Christopher Lentz in the TV series Zoo Doctor: My Mom the Vet. Since 2012 he has starred as Finn Kiesewetter in the TV series Morden im Norden. Sven married German actress Xenia Seeberg in 2003 but they have since separated. He has a total of six children from five different women.