Commissioned as a major in the First Georgia, Olmstead was promoted to colonel in December 1861. He served through the bombardment of Fort Pulaski, in which he commanded the Confederate forces. Olmstead served through the defense of Charleston. He was transferred to the in the Army of Tennessee in 1864, with which he served as a brigade commander during the remainder of the Atlanta campaign and its siege. Finally, he led a regiment under Hood, until he was put in charge of a brigade at Franklin. He finished the war in command of the First Georgia Consolidated, under Johnston, against Sherman until Johnston was forced to surrender.
