He led a brigade under Francis J. Herron at the Battle of Prairie Grove and, for his performance there, was promoted to brigadier general postdated to 29 November 1862.

Herron's division was transferred to the Army of the Tennessee and Orme continued in command of his brigade during the Siege of Vicksburg.

Upon the Confederate surrender, Orme's brigade led the Union army into the fallen the city.

His brigade was transferred to the Department of the Gulf but he was soon forced relinquish his command due to failing health.

A bronze marker in Orme's honor was erected in 1917 at Vicksburg National Military Park