Born into a noble family, he began military service during the Seven Years' War, rising to the rank of captain at age 23.
Serving first in the Regiment von Ysenburg, he fought at Hastenbeck, Sandersburg, and Lutterberg before transferring to the Jäger corps.
In October of that year he took over command of the entire Jäger corps after its leader, Carl von Donop, was killed in the Battle of Red Bank.
His corps performed with distinction in the Battle of Germantown, and guarded the rear of the British move from Philadelphia to New York City in 1778.
In 1805, under threat from Napoleon's armies, the elector again mobilized his forces, concentrating them under von Wurmb's command in Kassel.
Faced with overwhelming force in 1806, the elector fled, and Napoleon installed his brother Jérome as the new King of Westphalia.