In 19th August, 1854, Spotted Tail, led an attack on a mail wagon on its way to Salt Lake City. Lieutenant John L. Grattan and his men were killed during the fighting. Spotted Tail was caught on 18th October but after spending time at Fort Laramie and Leavenworth was allowed to go free. This experience turned him into the leader of the peace faction of the Sioux tribe.
In March 1866 Spotted Tail began negotiations at Fort Laramie and eventually signed a peace treaty with the American government on 27th June, 1866. As a result Spotted Tail and his followers were given permission to hunt buffalo along the Republican River.
In 1868 Spotted Tail signed another treaty. Unable to read the document he was fooled into signing away Sioux lands along the Republican and the Platte. The Sioux were now forced to move 30 miles to the west. Unhappy with his leadership, on 29th October, 1869, a group led by Big Mouth, tried to kill Spotted Tail. He survived the attack and Big Mouth was executed.
In 1870 Spotted Tail and Red Cloud visited Washington where peace negotiations led to the Sioux being allowed to move to the upper White River. In 1873 Spotted Tail took part in a raid on a Pawnee camp that resulted in the deaths of over 100 men.
Spotted Tail kept his followers out of the hostilities that led to the battle of Little Bighorn. However, later that year he was forced to sign a treaty that gave away the Black Hills of Dakota to the American government.
Spotted Tail was murdered by Crow Dog on 5th August, 1881.