He graduated from the United States Military Academy at West Point, New York, in 1850, and was commissioned as a second lieutenant.

Promoted to major in the new 16th U.S. Infantry Regiment in May 1861, he was attached to General Buell's command and took part in the Corinth campaign and the relief of Nashville.

He led his battalion into the Battle of Stones River in December, receiving a wound that incapacitated him for the rest of the war.

[1] In 1861, a temporary earthwork, Fort Slemmer, for part of the Civil War Defenses of Washington, D.C. was named after him.

[5] He died while in command of Fort Laramie from lingering effects of typhoid fever that he had contracted during the Civil War.