The regiment began organizing in August 1862 but recruiting problems delayed its entry into federal service until March 1863.

Predominantly from the Lake Michigan shore counties of the state, the regiment was mainly composed of German immigrants.

The 27th Wisconsin played a supporting role in the Siege of Vicksburg and participated in the capture of Little Rock, Arkansas during the year.

The regiment served in the Little Rock garrison and saw its first serious combat in the Camden Expedition of 1864, during which it fought in the Battle of Jenkins' Ferry.

By the time these incentives expired on August 22, only seven companies of the regiment had been organized mostly in Sheboygan and Manitowoc Counties.

German immigrants formed more than half of the regiment but it also included Irishmen and the Norwegian Company H.[1][2] With the last three companies organized, the regiment was mustered into federal service on March 7, 1863, under the command of Sheboygan lawyer and German Forty-Eighter Colonel Conrad Krez, and left Wisconsin for Columbus, Kentucky on March 16.

[12] The regiment moved four miles to Snyder's Bluff on June 11, forming part of the outer siege lines.

At Little Rock, the regiment was involved in garrison and picket duty with occasional forays into the region surrounding the city.

[13] Part of Adolph Engelmann's 3rd Brigade of Frederick Salomon's 3rd Division of Steele's VII Corps, the 27th Wisconsin participated in the Camden Expedition.

After Ritter's brigade arrived, Englemann continued to Hollywood and rejoined the division near Elkins' Ferry on April 5.

[8] In a letter home, Private Daniel Carver of Company B commented that "we would be better off" if the original officers left since these "do not amount to any great sum, in fact they are a damage to the Regt.

"[18] The regiment descended the Arkansas River to Pine Bluff on October 3 to reinforce the garrison, threatened by Magruder's superior forces.

[16] Like most other Wisconsin units, the 27th overwhelmingly supported Lincoln in the 1864 presidential election, although the regiment's home counties voted for McClellan.

The regiment lost five killed and five wounded during picket and fatigue duty before the Confederates evacuated the fort on the night of April 8.

Beginning on April 19, the regiment marched at least fifty miles up the Tombigbee River to McIntosh's Bluff to build fortifications.

[24] After Confederate general Richard Taylor surrendered his forces in the region, the fortifications were rendered unnecessary and the regiment was transported back to Mobile on May 9.

[6] After several weeks in camp near Mobile, the regiment was embarked for the voyage across the Gulf of Mexico to occupy Texas on June 1.

The regiment finished its active service there conducting picket and guard duty on the Mexican border before being sent to Brownsville for mustering out on August 2.