He was Field Marshal, president of the Hofkriegsrat, and the representative of the Emperor in the Perpetual Diet of Regensburg.

In 1665, he commanded an Austrian auxiliary force in the Spanish Netherlands, despite objections by Louis XIV.

On behalf of the Marquis de Castrel Rodrigo, the Spanish governor, he travelled to Berlin to negotiate an alliance against France with Elector Frederick William of Brandenburg.

In 1671, the Franco-Dutch War was foreseeable and Hermann was significantly involved in negotiations towards an alliance between Sweden and the Holy Roman Empire.

Hermann and Margrave Frederick VI of Baden-Durlach successfully besieged Philippsburg.

After the Treaty of Nijmegen ended the Franco-Dutch war, Hermann again acted as the Emperor's envoy to various courts.

When the Turkish army approached Vienna, Hermann requested permission to stay in the city.

On 3 September 1683, he represented the Emperor in a meeting of the great council of war, with King John III Sobieski of Poland and other allies.

At the behest of the Duke of Lorraine, the Emperor sent Hermann to Buda, where he was only able to save the remnants of the imperial army.

In 1687, Antonio Caraffa accused Hermann of making common cause with the Hungarian rebels.

On 9 December 1687, Hermann was present when Archduke Joseph I was crowned as King of Hungary in Bratislava.