He served both as a cavalry and as an infantry officer in the Union Army within the Trans-Mississippi Theater during the American Civil War, and was breveted a brigadier general near the end of the conflict.

Williams also helped organize and was the initial commander of the 1st Kansas Colored Infantry Regiment, the first unit of USCT soldiers to see combat.

Following the war, Williams remained a soldier until resigning in 1871 to become a rancher, then re-entered the service briefly about twenty years later, and afterwards became a merchant.

He led his regiment into battle on October 29 during the Skirmish at Island Mound in Bates County, Missouri, the first instance of Union Army colored soldiers in action.

[2] Williams died in Washington, D.C., on February 15, 1907, and was buried with full military honors in Arlington National Cemetery in Virginia.