After his Abitur in 1913, Leber studied national economics and history in Strasbourg (then Straßburg, Germany) and at the University of Freiburg im Breisgau.

As a soldier, Leber was wounded twice, promoted to lieutenant, and served after the war in the Reichswehr (regular army) with border security troops in the east.

[1] Adolf Hitler seized power in 1933, after which there was an attempt on Leber's life; he was detained, released after pressure from his Lübeck colleagues, and then arrested anew in March.

He was arrested by the Gestapo on 5 July 1944, fifteen days before Stauffenberg's attempt on Hitler's life in the Wolf's Lair in East Prussia.

On 20 October, Leber was accused in a trial before the Volksgerichtshof alongside Adolf Reichwein, Hermann Maass and Gustav Dahrendorf.

[3] On 5 November 1991, the German Post Office issued a postage stamp commemorating the 100th anniversary of Leber's birth.