Peter Osterhaus was born in Germany in 1823. After graduating from military school in Berlin Osterhaus took part in the 1848 German Revolution and was afterwards forced to flee the country. Osterhaus emigrated to the United States and became a bookkeeper in Missouri.

On the outbreak of the American Civil War he joined the Union Army. He was soon promoted to the rank of colonel and given command of the Southwest Missouri. Appointed brigadier general in June, 1862, during the Vicksburg Campaign, he commanded the 9th Division of the Army of Tennessee. Osterhaus obtained the rank of major general in July, 1864.

Osterhaus served as Consul to France (1866-77) and Vice-Counsul at Mannheim, Germany (1898-1900). Peter Osterhaus died in 1917.