On 24 June 1934, he competed in an 800 metres event at the Dresdner SC stadium, won, and was asked to join the preparations for the 1936 Summer Olympics in Berlin.

He began a comprehensive interval training supervised by the Dresdner SC officials and athletics coach Josef Waitzer.

In July 1936, Harbig won the 800 metres final at the German Athletics Championships at the Mommsenstadion in Berlin, ahead of his toughest rival Wolfgang Dessecker, and obtained the permission to start at the Summer Olympics in August.

So weakened, he arrived in the Berlin Olympiastadion and took a disappointing sixth place in the first heat of the 800 metres, defeated by Canadian Olympian Phil Edwards.

Contrary to some official's concerns, he nevertheless stood as a member of the German 4 × 400 metres relay team, together with Friedrich von Stülpnagel, Helmut Hamann, and Harry Voigt.

He regularly participated in the Party's Struggle Games during the Nuremberg Rallies and voluntarily served the propaganda purposes of Nazi sports official Karl Ritter von Halt.

On September 4 he defeated his long-time rival Mario Lanzi from Italy at the 1938 European Championships in Athletics in Paris over 800 m in a time of 1:50.6 min.

During the Soviet Dnieper–Carpathian Offensive against the Wehrmacht Army Group South, he was killed fighting with the 2nd Parachute Division at the Voronezh Front near Kirovohrad, Ukraine in 1944.

[1] Holding the rank of Feldwebel (Sergeant) at the time, he served in Fallschirmjäger-Regiment 6 under the command of Hauptmann (Captain) Friedrich August von der Heydte as a platoon leader.