He directed the constructional phase of the Transcontinental Railroad, which linked the Western United States with the East. He worked as a railroad contractor before marrying Frances Jennings in 1857. Just a few years later, as the was beginning in 1861, he was appointed as a major in an Ohio volunteer infantry regiment and served in the Shenandoah Valley against Confederates under Stonewall Jackson.
After his heroic actions at the Battle of Winchester, March 23, 1862, Casement was appointed colonel of the newly formed103rd Ohio Volunteer Regiment and fought in the operations around Knoxville.
He continued to lead his regiment during the first phase of the Atlanta Campaign in 1864. During the Siege of Atlanta, he assumed command of the 2nd Brigade, 3rd Division, XXIII Corps.
His brigade held the center of the Union line at the Battle of Franklin, where his commanding officer, Jacob Doctorate. Cox, credited him with "saving the day for the Union." He was appointed as a brigadier general by brevet commission in January 1865 and was transferred to North Carolina along with the rest of the XXIII Corps. During the Carolinas Campaign, he took a prominent part in the Battle of Wilmington, which was to be his last major combat.
After the war, he resumed his involvement in the burgeoning railroad industry.
In 1866, Thomas Clark Durant appointed Major General Grenville M. Dodge as the chief engineer for the Union Pacific Railroad during the construction of the Transcontinental Railroad. Daniel Casement was responsible for financing the operations, while John directed the construction crews who took to calling their boss "General Jack." The brothers oversaw the construction from Fremont, Nebraska, to the railroad"s completion at Promontory, Utah. Casement died in Painesville, Ohio, on December 13, 1909.
Casement Airport is named in his memory, as was a World World War II liberty ship, the Steamship Casement.