Karl was born on the 17th of March 1871, in Germany and information surrounding his emigration to the US and enlistment into the US Navy in 1895 are unknown. It is known that he deployed as a Coxswain to China in support of the Boxer Rebellion and his actions earned him the Medal of Honor. The citation reads:

In action with the relief expedition of the Allied forces in China, 13, 20, 21, and 22 June 1900. During this period and in the presence of the enemy, Thomas distinguished himself by meritorious conduct.

Karl is listed as receiving the Medal shortly after the dates listed in his citation, however, Karl Thomas died on the 18th of July 1900 in a field hospital at the age of 29. He was returned to the States and is buried in the San Francisco National Cemetery: Section NA-369.