He won the championship in his debut year in 1986 driving a Rover Vitesse, and raced an Alfa Romeo 75 in 1987. Despite not winning a second title, he remained one of the series' top drivers for the next decade as a Mercedes-Benz driver. He joined the AMG team in 1988, then Zakspeed in 1992, and returned to AMG in 1996, resulting runner-up in 1992, third in 1990, fourth in 1989 and 1995, fifth in 1994, and sixth in 1993. He collected 19 wins during his DTM career.
After the series was discontinued after 1996, he raced in several other touring car categories, including the German Supertouring Championship and the Danish Touring Car Championship, where he won a title in 2002.
- Watkins, Gary (14 August 2013). "Thiim to replace late Simonsen in Interlagos WEC round". autosport.com. Retrieved 22 September 2013.
|German Formula Three champion