Ord was commissioned as a second lieutenant in the Third Artillery Regiment after graduating from West Point in 1839. Ord was promoted to captain in 1850 while serving in the Pacific northwest.
Ord was promoted to the rank of major general and commanded the 2nd Division at Corinth. Although he was seriously wounded at Hatchie, Mississippi, he returned to duty and commanded the XIII Corps during last part of the Vicksburg campaign. During the Richmond-Petersburg campaign he commanded the XVIII Corps and was seriously wounded in the attack on Fort Harrison. He was in command of the Army of the James during the Appomattox campaign.