In Cologne he became acquainted with some of the more radical German political groups and was an active participant in the 1848 revolution, but was disillusioned by the outcome of the peace treaty that ended the First Schleswig War.

[5] Here he maintained his association with the Forty-Eighters, a group of military officers in the failed revolutions of 1848 who had fled to the United States; many ended up serving in the Union Army.

At the subsequent Battle of Gettysburg, Schimmelfennig commanded a brigade in fellow Forty-Eighter-turned-major general Carl Schurz's 3rd Division of the XI Corps.

His brigade suffered greatly, mostly due to a high prisoner rate as hundreds of men became confused in the narrow streets of Gettysburg and ended up being captured by oncoming Confederates.

During the retreat through the town, Schimmelfennig briefly hid in a culvert on Baltimore Street, and then stayed for several days in a shed on the Henry and Catherine Garlach property,[7] avoiding capture.

During his time of service in the swamps about Charleston, he contracted a virulent form of tuberculosis[9] which ultimately led to his death in Wernersville, Pennsylvania, where he visited a mineral springs sanatorium in an effort to find a cure.