In 1992 he began at the age of ten years in the German Kartszene and in 1997, won the junior class.

For the team Palfinger he finished 4th place twice, including once at Hockenheim supporting the German Grand Prix.

In 2007 he drove for Kruse Motorsport in the LMP2 class in the Le Mans Endurance Series finishing fifth place at Monza.

He made his debut in the Le Mans 24 Hours, again in a Kruse Motorsport Pescarolo-Judd, ending with an engine failure after 98 laps.

Towards the end of the 2007 season, Siedler joined ADM Motorsport in the new racing series International Formula Master.