<font face="Tahoma" size="2">Born in Dortmund. His father was the sales manager for the local Mercedes-Benz dealer. Hartmann was first spotted in 1935, driving off-road races with a Mercedes-Benz and became a reserve driver for the works Mercedes-Benz team 1937.
It was not until 1939 that he got to start his only Grand Prix for Mercedes-Benz as the fourth driver. Driving a Mercedes-Benz W154 in the Swiss Grand Prix at Bremgarten, he qualified 8th and finished 6th.
He drove 1500cc sports cars for Borgward. Racing in the Großer Nürburgring Jubiläumspreis at the Ring on August 3rd 1952, Hartmann came second in his 1500 cc Borgward and won his class, beating the Porsches. The race was won by Paul Pietsch in his Veritas. He also won the Grenzlandring Rennen on August 8th 1952, this time beating Pietsch's Veritas. His second win that year was at the Avus Rennen on September 28th. He won the 1500cc race beating Helm Glöckler's Porsche and his team-mate Adolf Brudes.
In 1953 at the Carrera Panamericana in Mexico, he took the lead in stage six and had a good lead in stage seven howver on the last stage his car dropped onto three cylinders and though he made the finish at Ciudad Juarez, he was outside the time limit by seven seconds and was therefore disqualified. He had driven for 3000 miles through Mexico, for nothing.
In 1954 he finished second in the 1500 cc race at the "Eifelrennen" behind Karl Günther Bechem.