Unlike many generals who led during the Civil War, Franz Sigel gained his leadership experience from his service in the army of his home country, Baden (modern day Germany). He graduated from the Karlsruhe Military Academy in 1843, and was commissioned as a lieutenant in the Baden Army. He participated in the 1848 Revolution which spread throughout many of the small Germanic countries, and fled from Prussian suppression, eventually moving to New York.

Shortly after the outbreak of the Civil War, Sigel became a colonel with the 3rd Missouri, where he fought under General Nathaniel Lyon. He led his troops in skirmishes near Camp Jackson, in St. Louis, and in Carthage, Missouri, establishing Federal control of the area. On August 7, 1861, he was promoted to brigadier general, partly as a tool to help recruit German-Americans into the Union Army. His best leadership during the war came at the Battle of Pea Ridge in Arkansas, where his command of two divisions helped secure a Union victory. Following the Battle of Pea Ridge, Sigel fought unsuccessfully throughout the rest of the war. He commanded during the Second Battle of Manassas, where the Union army was defeated, and remained in reserve at the battles of Fredericksburg and Antietam. He was defeated at the Battle of New Market, and resigned his commission on May 4, 1865.