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. Dodge hired Casement and his brother Daniel to direct the construction crews. Daniel T. 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.