Born in Germany, Sigel graduated at the military academy of Carlsruhe in 1841, and served as an officer in the regular army until 1847, when he resigned his commission. In 1848-90 he took side with the people in the revolutionary struggles of the period. He afterward lived successively in Switzerland, Italy, France and England, until 1852, when he sailed to America, landing in New York.

In 1857 he went to St. Louis, where he held the position of professor of mathematics, American history and French at the German-American Institute of that city; and was also elected director of the St. Louis public schools in 1860.

At the outbreak of the civil war, Sigel resigned these positions, and organized a regiment of infantry, a battalion of artillery of three batteries, and a squadron of cavalry. He commanded the expedition to southwest Missouri, and fought the battle of Carthage with eight hundred against four thousand men.

Gen. Sigel also commanded a brigade in the battle of Wilson's Creek under Gen. Lyon, a division in the campaign of Gen. Fremont, and two divisions in the battle of Pea Ridge.

He was ordered to the East in May, 1862, and commanded a division at Harper's Ferry, and the first corps of the army of Virginia, under Pope, in the battle of Bull Run on August 28-30.

After serving throughout the war, he resigned from the army in 1865. He has filled numerous civil positions, and was a republican in politics until 1876, at that time declaring for Tilden; and he has advocated the policy of the democratic party since that time.

From 1881 to 1885 Gen. Sigel lectured in English and German, and also edited a weekly paper. In 1887 he was appointed pension agent, by President Cleveland, for the city of New York.