Having followed a runner-up finish in the ADAC Procar series in 2006 up with three race-winning seasons in the Mini Challenge Germany, Keilwitz entered the ADAC GT Masters in 2009 with Leipert Motorsport. He went on to triumph in the FIA GT3 European Championship the following year, winning four races at Callaway Competition alongside Christian Hohenadel.[3][4] Keilwitz and the team migrated to GT Masters from 2011 onward, finishing second in 2012 before triumphing overall in 2013.[5] He competed in the series until 2021, finishing third thrice and second in 2018.
During his career, the German has taken part in the Nürburgring 24 Hours on a number of occasions. Aside from his record lap in 2023, Keilwitz finished second in the SP8 class in 2011 and won the 2023 contest whilst driving in the SP9 Pro-Am category in a Ferrari 296 GT3 fielded by WTM by Rinaldi Racing.[7]