Hermann Thomsen was born on 10 March 1867 in Flensburg which had recently been lost by the Kingdom of Denmark and incorporated into Prussia.

In March 1915, von der Lieth-Thomsen was appointed Chief of Field Air Forces (Chef des Feldflugwesens) for the German Army.

In 1917, von der Lieth-Thomsen was awarded the Pour le Mérite even though as a senior commander he was not directly involved in air combat.

His son, Joachim von der Lieth-Thomsen, was hit by anti-aircraft fire from a ship while he was flying over the Thames Estuary in July 1917 and died a few days before the armistice as a POW.

In the 1920s, Lieth-Thomsen actively participated in the German efforts to build a secret Air Force in the Soviet Union.